Concurring Opinion by
Mr. Justice Roberts :I concur in the judgment of the Court. The disposition of appellant’s claim is governed by this Court’s decision in Commonwealth v. Phila. Life Assurance Co., 419 Pa. 370, 214 A. 2d 209 (1965), appeal dismissed for want of a substantial federal question, 384 U.S. 268, 86 S. Ct. 1476 (1966).
Life Assurance, like the instant case, involved a constitutional attack on the very statute at issue here, the *164act of February 21, 1961.1 As part of that challenge this Court construed the Act of 1961. In doing so we stated: “[T]he receipt of renewal premiums in practical effect amounts to no more than the resale of insurance coverage for an additional period of time. As the court below noted, ‘[an insurance company’s] business is broader than just selling policies; it also extends to the collection of premiums whether in the year in which the policy is sold initially or in subsequent years on the renewal of the policy.’ ” Id. at 390, 214 A. 2d 221 (footnote omitted). The plain meaning of our holding in Life Assurance is that the Act of 1961 does not impose a retroactive tax. Although it is true that the contracts in question were written before 1961, it is the receipt of revenue during each tax year, not the writing of contracts, that produces the taxable event.
In order for a taxpayer to demonstrate that a tax is unconstitutionally retroactive, he must first prove that it is in fact retroactive. Appellant cannot prevail on this determinative issue, because this Court has already decided it adversely to appellant.
Since Life Assurance controls the outcome of this litigation, it is not necessary here to consider whether *165appellant’s participation as amicus curiae at tte trial and appellate levels in Life Assurance2 is sufficient to bring into play tbe doctrine of collateral estoppel.
Mr. Justice Manderino joins in this concurring opinion.Act of February 21, 1961, P. L. 33, §§1-10, as amended, Act of March 4, 1971, P. L. 6, art IX, §§901-06, 72 P.S. §§7901-06 (Supp. 1973).
The Act of 1961 by taxing gross receipts imposed a tax on the privilege of doing insurance business within the Commonwealth. The tax was not predicated on the taxpayer’s earnings or ability to pay and was due regardless of whether the taxpayer’s business generated income or profits during the tax year. This is apparent from the specific language of the statute. Id. §2. See F. J. Busse Co. v. Pittsburgh, 443 Pa. 349, 353 n.1, 279 A. 2d 14, 16 n.1 (1971); Commonwealth v. Kirby Estates, Inc., 432 Pa. 103, 108, 246 A. 2d 120, 122 (1968) (Roberts, J., dissenting); Commonwealth v. Columbia Gas & Elec. Corp., 336 Pa. 209, 217-22, 8 A. 2d 404, 410-12 (1939); Insurance Co. of North America v. Commonwealth, 87 Pa. 173, 182 (1878). Cf. Penn Mutual Indemnity Co. v. Commissioner, 277 F. 2d 16 (3d Cir. 1960).
In this earlier litigation challenging the constitutionality of the Act of 1961, appellant filed a brief as amicus curiae in and argued before both the Dauphin County Court sitting as the Commonwealth Court and this Court. See Commonwealth v. Phila. Life Assurance Co., 419 Pa. 370, 214 A. 2d 209 (1965), aff’g 35 Pa. D. & C. 2d 390 (C. P. Dauphin County 1964).