Yes, Congress may tax "occupations of common law right" and has done so many times, for example the Social Security tax and the Federal income tax.

The argument has been made that earning a living is a right, sometimes called a "God given right" or a "common law right," and not a privilege and therefore it can not be taxed. Sometimes those presenting this argument would distinguish between natural occupations, i.e. farmer or rancher, and occupations created by the government, i.e. government employee or lawyer, the later being taxable while the others are not. These types of distinctions have never been recognized in the area of taxing power of the states or the Federal government. The Supreme Court has specifically rejected a challenge to the Social Security tax based on this type of argument, stating:

The statute books of the states are strewn with illustrations of taxes laid on occupations pursued of common right. We find no basis for a holding that the power in that regard which belongs by accepted practice to the legislatures of the states, has been denied by the Constitution to the Congress of the nation.100

In challenges to the Federal income tax, the courts have consistently rejected the claim that Congress may not tax occupations of common law right.101
 

100 Steward Machine C0. v. Davis, 301 U.S. 548 at 582 to 583 (1937).

101 See, for example, United States v. Russell, 585 F.2d 368 (8th Cir.1978); United States v. Silkman, 543 F.2d 1218 (8th Cir.1976), cert. denied, 431 U.S. 919 (1977); and Jones v. United States, 551 F. Supp. 578 (N.D.N.Y.1982).