A colleague asked me this, and a Google search suggests others have been asking the same question as well. Here's a short summary:

1. The Constitutions bans both the federal and state legislatures from enacting "bills of attainder."

2. This is understood as barring "a legislative act which inflicts punishment without a judicial trial." ("If the punishment be less than death, the act [was historically] termed a bill of pains and penalties," but "[w]ithin the meaning of the Constitution, bills of attainder include bills of pains and penalties.") So if Congress says, "We conclude that Eugene Volokh is guilty of treason, and we order him to be executed," that would be a classic bill of attainder.

3. According to the Court, permanent exclusion of named people -- or even a class of people, such as Communist Party members or people who had given help to the Confederacy -- from government office may constitute "punishment" and be treated as an unconstitutional Bill of Attainder. See U.S. v. Lovett (1946), U.S. v. Brown (1965), and Cummings v. Missouri (1866).

4. This may apply to punishment of corporations and other entities, and not just of individuals, at least according to Consolidated Edison Co. v. Pataki (2d Cir. 2002); I think that has to be right, but the issue is not clearly settled.

5. At the same time, even legislation that singles out individuals is not a Bill of Attainder if "the law under challenge, viewed in terms of the type and severity of burdens imposed, reasonably can be said to further nonpunitive legislative purposes." See Nixon v. Administrator of General Services (1977); SeaRiver Maritime Financial Holdings Inc. v. Mineta (9th Cir. 2002) (upholding the legislative exclusion of "any vessel that spilled more than one million gallons of oil into the marine environment after March 22, 1989" -- a class that includes only the Exxon Valdez -- from Prince William Sound, because it has the legitimate nonpunitive purpose of "reduc[ing] the environmental risk to the Sound" by excluding "a vessel with a history of substantial spillage, and encourag[ing] SeaRiver and other tank vessel owners to take greater steps to avoid a similar spill in any marine environment").

But the trouble, of course, is that most laws, including punitive ones, also further nonpunitive legislative purposes. The hypothetical Eugene Volokh Execution Act of 2009 would further nonpunitive legislative purposes of preventing future bad acts by me (as well as punishing me for all my manifold past sins). Likewise, the permanent exclusion of certain people from federal employment, struck down in Lovett and Brown, was likely aimed at preventing bad behavior by the named employees (Lovett) and Communist employees (Brown).

So would defunding ACORN be an unconstitutional bill of attainder? My rereading of the precedents leads me to confidently and unambiguously say, "I don't know." The distinction between "punishment" and actions that "reasonably can be said to further nonpunitive legislative purposes" strikes me as generally elusive and perhaps even illusory, and especially so here. But I thought I'd lay out the basic questions and precedents, and see what the rest of you think.

Here's the report, published Tuesday. An excerpt from the Summary:

The two main criteria which the courts would likely look to in order to determine whether legislation is a bill of attainder are (1) whether "specific" individuals or entities are affected by the statute, and (2) whether the legislation inflicts a "punishment" on those individuals. Under the instant bills, the fact that ACORN and its affiliates are named in the legislation for differential treatment would appear to meet a per se criteria for specificity.

The U.S. Supreme Court has also 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 are the "functional equivalent" of punishment because they cannot reasonably be said to further "non-punitive legislative purposes;" and (3) where the legislative record evinces a "congressional intent to punish." The withholding of federal contracts or grants does not appear to be a "traditional" punishment, nor does the legislative record so far appear to clearly evince an intent to punish. The question of whether the instant legislation serves as the functional equivalent of a punishment, however, is more difficult to ascertain.

While the regulatory purpose of ensuring that federal funds are properly spent is a legitimate one, it is not clear that imposing a permanent government-wide ban on contracting with or providing grants to ACORN fits that purpose, at least when the ban is applied to ACORN and its affiliates jointly and severally. In theory, under the House bill, the behavior of a single employee from a single affiliate could affect not only ACORN but all of its 361 affiliates. Thus, there may be issues raised by characterizing this legislation as purely regulatory in nature. While the Supreme Court has noted that the courts will generally defer to Congress as to the regulatory purpose of a statute absent clear proof of punitive intent, there appear to be potential issues raised with attempting to find a rational non-punitive regulatory purpose for this legislation. Thus, it appears that a court may have a sufficient basis to overcome the presumption of constitutionality, and find that it violates the prohibition against bills of attainder.

My much more tentative thoughts on the subject are here.