First I thought that the proposals to tax back bonuses from AIG would be unconstitutional for bill of attainder reasons. Then Larry Tribe convinced me that it would be easy to design a tax bill that passed constitutional muster. But now I see that the Congressional Research Service has issued a report (pdf) on the constitutional implications of the tax clawback proposals, which concludes that "the strongest arguments against their constitutionality seem to arise under the bill of attainder analysis." So I'm going to give up on the question and just paste their test after the jump:
The two main criteria that the courts will look to in order to determine whether legislation is a bill of attainder are (1) whether specific individuals are affected by the statute ("specificity" prong), and (2) whether the legislation inflicts a punishment on those individuals ("punishment" prong). The Supreme Court has identified three types of legislation which would fulfill the "punishment" prong of the test: (1) where the burden is such as has "traditionally" been found to be punitive, (2) where the type and severity of burdens imposed cannot reasonably be said to further "nonpunitive legislative purposes," and (3) where the legislative record evinces a "congressional intent to punish."
You can decide whether these two prongs will skewer the House bill.
But more generally, I agree with Matt Yglesias that the focus on taxing back "bonuses" is still a silly semantic quibble, regardless of the constitutional implications. Sure, I think there are good arguments against capping compensation at all. But if we're going to get into the business of doing it I would prefer to see Congress do so on the basis of some general principle and not on the basis of a a single word ("bonus") that policymakers and the public find offensive and scary. Why not just christen bonuses "annual lump salaries" and avoid the trouble of passing a law?