This case raises the question whether Public Acts 1979, No. 79-422, which permits a service fee agreement to be included in collective bargaining agreements, is applicable to teachers whose contracts of employment antedated the act. The trial court held that it was not applicable. We disagree.

The plaintiffs, Gloria Dowaliby and Hartford Education Association, brought this action against Hartford Federation of Teachers and the board of education of the city of Hartford, originally seeking to enjoin the defendants from enforcing a provision1 in the collective bargaining agreement entered into by the defendants which authorized the board to deduct a representation fee from the plaintiff Dowaliby’s salary. The complaint was later amended to seek a judgment declaring that this “agency shop” provision violates General Statutes § 10-153a and the National Labor Eelations Act, 29 U.S.C. § 186 (c) (4). While the action was pending the General Assembly enacted Public Acts 1979, *461No. 79-422, which became effective October 1, 1979. On July 25, 1979, the trial court rendered a judgment declaring that the agency shop clause was illegal when made on July 1, 1979, both under state and federal statutes, and could not be enforced against the plaintiffs and that the plaintiffs could not be required to contribute, directly or through withholding, a “service fee” as a condition of employment during the life of any employment contract entered into prior to October 1, 1979.

The trial court concluded that the agency shop clause violates 29 U.S.C. §186 (c) (4), which concerns payments, loans and gifts made by an employer to a labor organization including payments so made as a result of deductions from employees’ wages. We need not examine this claim in depth because states and political subdivisions thereof are expressly excluded from the definition of “employer” as that term is used in the Labor-Management Relations Act of 1947, 29 U.S.C. §§ 141-187. 29 U.S.C. § 142 (3), § 152 (2). See also Bus Employees Division 998 v. Wisconsin Employment Relations Board, 340 U.S. 383, 398 n.25, 71 S. Ct. 359, 95 L. Ed. 364 (1951).

General Statutes § 10-153a,2 before its amendment by Public Acts 1979, No. 79-422, protected members *462of the teaching profession who refused to join or assist any organization for professional or economic improvement. If we assume that this statute operated to bar the enforcement of agency shop clauses in collective bargaining agreements prior to October 1,1979, the question arises whether any such clauses became enforceable upon the effective date of the amendment.

If the agency shop clause was illegal in the sense that it was contrary to a deeply rooted public policy, it would be void at its inception. Hanford v. Connecticut Fair Assn., 92 Conn. 621, 623, 103 A. 838 (1918). The clause, however, does not offend the public policy of this state. Agency shop clauses have long been a part of collective bargaining in this country. See Hopfl, “The Agency Shop Question,” 49 Cornell L. Q. 478 (1964). Although the Connecticut Teacher Negotiation Act; § 10-153a through 153j; does not mirror federal law, resort to the policies underlying federal law is often useful in discerning the contours of our own labor policy. See West Hartford Education Assn. v. DeCourcy, 162 Conn. 566, 578-79, 295 A.2d 526 (1972). The National Labor Relations Act, particularly 29 U.S.C. § 158 (a) (3), has been construed as allowing agency shop clauses. NLRB v. General Motors Corporation, 373 U.S. 734, 741, 83 S. Ct. 1453, 10 L. Ed. 2d 670 (1963). In Connecticut, union shop clauses, which are more restrictive than the agency shop provisions, are expressly provided for in the private sector by General Statutes § 31-105 (5). In light of the foregoing we conclude that, while the clause may have been prohibited by state statute when agreed to, it did not contravene public policy and, therefore, was not a nullity.

*463The clause was, at most, subject to the defense that § 10-153a barred its enforcement. After October 1, 1979, that defense was no longer available because Public Acts 1979, No. 79-4223 expressly provided that such clauses were enforceable in teacher contracts. Without that defense the contract is enforceable as the parties undeniably intended it to be, namely, with an agency shop clause.

The plaintiff questions whether consistent with the impairment of the obligation of contract clause of the United States constitution, article I, section 10, a state statute may validate an invalid provision of a contract. The short answer to this question is, it was ever thus. Satterlee v. Matthewson, 27 U.S. (2 Pet.) 380, 413 (1829); Welch v. Wadsworth, 30 Conn. 149, 155 (1861). The rights and obligations under the contract remain unchanged by the 1979 public act. The only change wrought by the public act concerns the availability of the defense that the clause violated § 10-153a. Upon the effective date of this statute, October 1, 1979, the agency clause provision became fully enforceable. See Beckman v. St. Louis County Board of Commissioners, 308 Minn. 129, 241 N.W.2d 302 (1976).

*464There is error, the judgment is set aside and the case is remanded with direction to render judgment consistent with this opinion.

In this opinion the other judges concurred.