The plaintiff appeals from a decision of the Appellate Tax Board upholding the commissioner’s denial of applications for abatemenf of sales taxes, totaling $97,565.38, assessed to the decedent taxpayer for the periods between January 1, 1985, and September 30, 1985, and between July 1, 1987, and March 31, 1990. We affirm.

During the relevant periods, the taxpayer was engaged in the business of reupholstering office chairs. In his reupholstering transactions, the taxpayer collected a sales tax from his customers for the cost of materials, but did not charge or collect sales tax on the cost of labor.

For both periods at issue, the taxpayer’s failure to collect a sales tax for the cost of labor was contrary to a regulation of the commissioner requiring a re-upholsterer to collect a sales tax that “applies to the total amount which the reupholsterer charges the customer, whether or not the reupholsterer states the material charge and labor charge separately in the bill" 2 (emphasis added).

The taxpayer responds only that the commissioner is estopped from enforcing the regulation regarding the sales tax. This is so, the taxpayer argues, because for a two-day period in 1991 — after the tax period in question in this case — there was in effect an emergency regulation defining “reupholstering services’’ as a “service” for purposes of the newly enacted statute unrelated to the sales tax — and which survived only briefly3 — taxing “services.”

There is no merit to the taxpayer’s position. It is enough to say here that “[ojnly with hesitation is the doctrine of estoppel invoked against the government in the exercise of its public duties.” Corea v. Assessors of Bedford, 384 Mass. 809, 809 (1981). This is especially so in tax matters where a taxpayer is *931entitled to an abatement “only if the tax is excessive in amount or illegal.” Commissioner of Rev. v. Marr Scaffolding Co., 414 Mass. 489, 494 (1993). If the commissioner has made a mistake, the commissioner should not be estopped from correcting that mistake, in “assessing a tax that is otherwise lawfully due.” Id. at 495, quoting from John S. Lane & Son, Inc. v. Commissioner of Rev., 396 Mass. 137, 140 (1985). The taxpayer makes no argument — aside from estoppel — that the tax assessed was illegal. Contrast Commissioner of Rev. v. BayBank Middlesex, 421 Mass. 736, 740-743 (1996) (the commissioner retroactively changed a long-established instruction sheet — which the taxpayer had followed for over forty years •— by a notice of assessment sent without warning and without a clear policy statement).

Decision of the Appellate Tax Board affirmed.