The defendant, AFSCME Council 93, Local 1703 (union), appeals from an amended judgment entered after an eight-day jury trial, awarding the plaintiff, James Blauvelt, significant damages1 on his claim against the union for breach of the duty of fair representation. For the reasons set out infra, we affirm.

Background. On March 13, 2001, the town of Bedford (town) held a hearing to determine what, if any, disciplinary measures it ought to take against five employees, including Blauvelt, based on allegations that each had falsified time records and defrauded the town. Blauvelt, like the others, was represented by the union under a collective bargaining agreement (CBA) then in place between the union and the town. Blauvelt was a fourteen year veteran of the town’s public works department.

Ultimately,2 the town manager sent a letter dated April 13, 2001, to the employees, including Blauvelt, of the town’s decision to terminate their employment, effective as of April 14, 2001. The letter was delivered by hand to Blauvelt on Monday, April 16, 2001, which was Patriots’ Day. The union office was closed that particular day, and union officials were not available to be reached for advice. Blauvelt spoke with a union official the following day, Tuesday, April 17.

On Friday, April 20, 2001, the union submitted written grievances, including one for Blauvelt, to the town to contest the job terminations. In turn, the town took the position that the griev-*796anees, including Blauvelt’s, were untimely, citing art. 7 of the CBA. Article 7, § 2, provides:

“[A] grievance involving discharge must be in writing and must be received by the Employer within three (3) working days from the date of discharge. In the event a grievance involving a discharge is not filed within such time, the discharge shall be deemed to be for just cause and shall not be subject to arbitration.”

Not deterred by the town’s stance, the union demanded arbitration, but the town was successful in having the arbitration stayed by a Superior Court judge.

After an unsuccessful petition to a single justice of this Court, a different Superior Court judge determined that the grievances had not been timely submitted to the town. From a corrected judgment that allowed the town’s stay application, the union pursued an appeal. See G. L. c. 150C, § 16. This court vacated the judgment of the Superior Court in favor of the town and remanded the case to the Superior Court for the entry of an order denying the stay application and directing the parties to proceed to arbitration. Bedford v. AFSCME Council 93, Local 1703, 69 Mass. App. Ct. 110, 111-112 (2007) (Bedford).3

While Bedford was pending, Blauvelt filed this action in Superior Court, claiming that the union had committed a breach of its duty of fair representation.4 The case was eventually tried to a jury, with the resulting verdict for the plaintiff. See note 1, supra.

On appeal, the union contends that it was entitled to plead the charitable immunity cap on damages provided by G. L. c. 231, § 85K, as an affirmative defense and that certain errors were made in the jury instructions and in the exclusion of evidence pertaining to its defense of superseding cause.5,6 We address first *797the issues raised by the union. We conclude by addressing the doctrine of primary jurisdiction, which we raised on our own initiative.

1. Charitable immunity cap. The union argues that it should have been granted leave to amend its answer in order to raise the statutory cap on damages imposed by G. L. c. 231, § 85K, as an affirmative defense. We review to determine whether the motion judge abused his considerable discretion in denying the motion. Harvard Law Sch. Coalition for Civil Rights v. President & Fellows of Harvard College, 413 Mass. 66, 72 (1992).

Section 85K limits tort liability of a charitable entity to $20,000. See, e.g., Keene v. Brigham & Women’s Hosp., Inc., 439 Mass. 223, 238-239 (2003); Ayash v. Dana-Farber Cancer Inst., 443 Mass. 367, 391, cert. denied sub nom. Globe Newspaper Co. v. Ayash, 546 U.S. 927 (2005). To be shielded by § 85K, a defendant must show: (a) it is a charity, and (b) the injury it may be held responsible for, under tort law principles, occurred in the course of activities that “accomplish directly” its charitable purposes.7 Conners v. Northeast Hosp. Corp., 439 Mass. 469, 479 (2003). “An institution will be classed as charitable if the dominant purpose of its work is for the public good and the work done for its members is but the means adopted for this purpose.” Harvard Community Health Plan, Inc. v. Assessors of Cambridge, 384 Mass. 536, 544 (1981), quoting from Massachusetts Med. Soc. v. Assessors of Boston, 340 Mass. 327, 332 (1960). Here, the union failed to demonstrate that it was a charity within the definition of the statute, rather than an organization existing for the primary benefit of its membership. The fact that the union’s activities are not inconsistent with *798broader public policy, as reflected in G. L. c. 150A, does not transform the union from an organization existing primarily for the benefit of its members into one existing primarily for the public good. Accordingly, the judge did not abuse his discretion in denying the union’s motion seeking leave to amend its answer to assert the defense. Keville v. McKeever, 42 Mass. App. Ct. 140, 149 (1997) (no abuse of discretion in denying motion to amend answer where amendment would have been futile).

2. Jury instructions. The union argues that the judge should have given a jury instruction that the “mere failure to meet a deadline, without more, is not evidence of inexcusable neglect” that constitutes a breach of the duty of fair representation. For this proposition, the union cites only to a case decided by the United States Court of Appeals for the Ninth Circuit, Patterson v. International Bhd. of Teamsters, Local 959, 121 F.3d 1345 (9th Cir. 1997), cert. denied, 523 U.S. 1106 (1998). We have carefully reviewed the Patterson decision and see nothing in it that stands for the proposition urged by the union. We note, too, that the case does not involve a claim brought under G. L. c. 150E.

To the extent that the union is also arguing that the jury instructions did not adequately inform the jury that mere negligence is not enough to constitute a breach of the duty of fair representation, that argument is without foundation in the record.8 The instructions were fully consistent with our cases defining the *799contours of a claim for breach of the duty of fair representation under G. L. c. 150E, § 10, and sufficiently apprised the jury that liability could not be predicated upon mere negligence. See Gon-calves v. Labor Relations Commn., 43 Mass. App. Ct. 289, 293 (1997), quoting from Graham v. Quincy Food Serv. Employees Assn. & Hosp., Library & Pub. Employees Union, 407 Mass. 601, 606 (1990) (“Unions are permitted ‘a wide range of reasonableness’ in representing the often-conflicting interests of employees; hence, unions are vested with considerable discretion not to pursue a grievance, as long as their actions are ‘not improperly motivated, arbitrary, perfunctory or demonstrative of inexcusable neglect’ ”).

3. Superseding cause. A few weeks after his discharge, Blau-velt suffered a stroke, which the union contends would have prevented him from returning to work, regardless of whether he had won reinstatement. Thus, the union concludes, Blauvelt’s medical condition was a superseding cause that limited his entitlement to damages. In this regard, the union makes three arguments: first, that the special verdict form should have included a question pertaining to superseding cause; second, that the judge erred when he limited the town manager’s testimony regarding the town’s practices relating to holding jobs open for sick employees; and third, that the union’s motion for judgment notwithstanding the verdict should have been granted given the evidence of Blau-velt’s medical condition.

“The nature, scope, and form of special questions submitted to a jury pursuant to Mass. R. Civ. P. 49(a), 365 Mass. 812 *800(1974), are matters within the discretion of the trial judge.” Everett v. Bucky Warren, Inc., 376 Mass. 280, 291 (1978). “We view the questions submitted to the jury in light of the instructions given by the judge.” Draghetti v. Chmielewski, 416 Mass. 808, 818 (1994). Here, the union concedes that the judge properly instructed the jury concerning superseding cause. “The instructions enabled the jury to understand their duty in answering the questions on the verdict form.” See id. at 818-819.9 There was no error in the judge’s refusal to include a separate question using the specific phrase “superseding cause.” Nor do we perceive any risk that the jury misunderstood their task with respect to awarding damages in the absence of such a separate question.

We are equally unpersuaded by the union’s argument that the trial judge incorrectly refused to permit the town manager to answer certain questions regarding the town’s policies for sick employees. The town manager was permitted to testify about a broad range of topics relating to the way that the town handles the absences of employees who are out for prolonged periods because of medical problems. On the ground that no foundation had been laid, however, the judge sustained objections to questions that sought the town’s “practice” in this regard. The judge was correct; no foundation had been laid that there was a practice because the situation had occurred only once before. *801Finally, viewing the evidence in the light most favorable to Blauvelt, and drawing all inferences from it in his favor, see, e.g., D’Annolfo v. Stoneham Hous. Authy., 375 Mass. 650, 657 (1978), we conclude that the judge did not err in denying the union’s motion for judgment notwithstanding the verdict. There was sufficient evidence to support the jury’s verdict that Blau-velt was not medically precluded from returning to work, including the testimony of Blauvelt’s expert, Dr. Aroesty.10

4. Primary jurisdiction. Although primary jurisdiction was pleaded by the union as an affirmative defense in its answer, the union did not further raise the issue either below or here on appeal. This appears to have been a deliberate, strategic abandonment of the doctrine: the union served a motion to dismiss based on the doctrine and received an opposition from the plaintiff under the packaging procedure of Superior Court Rule 9A (2004),11 but it neither filed that motion nor made any other attempt to dismiss or stay the Superior Court action in favor of proceeding before the Labor Relations Board (board). The Supreme Judicial Court has recently clarified that primary jurisdiction cannot be waived. Everett v. 357 Corp., 453 Mass. 585, 609 (2009). Accordingly, we address the doctrine on our own initiative, having requested and received submissions from the parties pursuant to Mass.R.A.P 16(1), as amended, 386 Mass. 1247 (1982), regarding the doctrine and its application to the circumstances of this case.

Where an agency has statutorily been granted exclusive authority over a particular issue, the doctrine of primary jurisdiction requires that a court refer the issue to the agency for adjudication in the first instance. Everett v. 357 Corp., supra at 609-610 (because Department of Transportation [DOT] has exclusive statutory authority over issue of truck driver qualification, doctrine of primary jurisdiction required that issue be referred to DOT and that Superior Court action be stayed). Where, however, no statute has conferred exclusive authority to the agency, *802primary jurisdiction is “a doctrine exercised in the discretion of the court.” Columbia Chiropractic Group, Inc. v. Trust Ins. Co., 430 Mass. 60, 62 (1999).

The legislative scheme of G. L. c. 150E contemplates a “primary,” but nonexclusive, role for the board in adjudicating cases concerning the duty of fair representation. Leahy v. Local 1526, Am. Fedn. of State, County, & Mun. Employees, 399 Mass. 341, 347 (1987). Thus, although a claim for breach of the duty of fair representation in most instances should be presented first to the board, ibid., referral to the agency may not be required depending on a number of factors, including whether the issue is of one within the particular expertise of the agency, whether there are factual issues to be resolved, and whether non-parties will be affected by the decision. Id. at 347-348 (after taking various case-specific factors into account, declining to dismiss action under primary jurisdiction doctrine). See Harrison v. Massachusetts Soc. of Professors/Facuity Staff Union/MTA/NEA, 405 Mass. 56, 59-60 (1989) (same); Graham v. Quincy Food Serv. Employees Assn. & Hosp., Library & Pub. Employees Union, 407 Mass. at 611 (same); Columbia Chiropractic Group, Inc. v. Trust Ins. Co., 430 Mass. 60, 62 & n.2 (1999) (same); Uniformed Firefighters of Ludlow, Local 1840 v. Selectmen of Ludlow, 29 Mass. App. Ct. 901, 902-904 (1990) (same).

Here, although we are convinced that the action should originally have been filed with the board,12 a number of factors convince us that, at this advanced stage of these proceedings, dismissal based on primary jurisdiction is not required.13 Among the factors militating against dismissal on the basis of primary jurisdiction are the union’s deliberate abandonment of the doctrine below, combined with the decision not to raise the issue on appeal. Although the doctrine cannot be waived, these strategic choices indicate that the union (a sophisticated litigant in this *803arena, fully familiar with the expertise and competence of the board) did not believe that the board’s expertise was necessary. In addition, we see no benefit (and the union has not identified any) in invoking this doctrine at this point in this litigation: the case has been fully tried to a jury, at significant cost to the Commonwealth, and the jury have already made credibility assessments and factual findings that are not being questioned and need not be revisited by the board. Further, at least one issue of law that has been raised — whether the union is entitled to the charitable immunity cap — does not involve the board’s special authority or expertise. Finally, we are concerned that a manifest injustice would occur were we to dismiss the case based on primary jurisdiction in light of the union’s position that the plaintiff’s claim would be time barred were it presented now to the board. See note 13, supra.

Although the Everett decision extensively discusses the doctrine of primary jurisdiction, the decision to remand the case to the Superior Court for the entry of a judgment of dismissal rested on the Supreme Judicial Court’s determination that there was a lack of subject matter jurisdiction pertaining to the claims. It was because of the absence of subject matter jurisdiction in that case that the court was compelled to employ the “drastic remedy” of directing that a judgment of dismissal enter after a jury had returned a verdict in favor of the plaintiff. As the court observed, “Seldom does an appeal present itself to us in a posture that requires us to nullify an entire, completed civil jury trial.” Everett v. 357 Corp., 453 Mass. at 611-612. Here, however, there is no absence of subject matter jurisdiction. After an eight-day jury trial in which neither the parties nor the judge sought to invoke the doctrine of primary jurisdiction, we will not exercise our discretion to nullify the amended judgment that entered in this case.

For the reasons set out supra, the amended judgment is affirmed.

So ordered.