Jack Balkin: jackbalkin at yahoo.com
Bruce Ackerman bruce.ackerman at yale.edu
Ian Ayres ian.ayres at yale.edu
Corey Brettschneider corey_brettschneider at brown.edu
Mary Dudziak mary.l.dudziak at emory.edu
Joey Fishkin joey.fishkin at gmail.com
Heather Gerken heather.gerken at yale.edu
Abbe Gluck abbe.gluck at yale.edu
Mark Graber mgraber at law.umaryland.edu
Stephen Griffin sgriffin at tulane.edu
Jonathan Hafetz jonathan.hafetz at shu.edu
Jeremy Kessler jkessler at law.columbia.edu
Andrew Koppelman akoppelman at law.northwestern.edu
Marty Lederman msl46 at law.georgetown.edu
Sanford Levinson slevinson at law.utexas.edu
David Luban david.luban at gmail.com
Gerard Magliocca gmaglioc at iupui.edu
Jason Mazzone mazzonej at illinois.edu
Linda McClain lmcclain at bu.edu
John Mikhail mikhail at law.georgetown.edu
Frank Pasquale pasquale.frank at gmail.com
Nate Persily npersily at gmail.com
Michael Stokes Paulsen michaelstokespaulsen at gmail.com
Deborah Pearlstein dpearlst at yu.edu
Rick Pildes rick.pildes at nyu.edu
David Pozen dpozen at law.columbia.edu
Richard Primus raprimus at umich.edu
K. Sabeel Rahmansabeel.rahman at brooklaw.edu
Alice Ristroph alice.ristroph at shu.edu
Neil Siegel siegel at law.duke.edu
David Super david.super at law.georgetown.edu
Brian Tamanaha btamanaha at wulaw.wustl.edu
Nelson Tebbe nelson.tebbe at brooklaw.edu
Mark Tushnet mtushnet at law.harvard.edu
Adam Winkler winkler at ucla.edu
The short answer is that the current plans from both the House and the Senate appear to be constitutional. The House plan is here; a summary of the Senate plan is here. There are five possible constitutional limitations that might be relevant.
There is no problem under the Due Process Clause of the Fifth Amendment because the tax is rationally related to a legitimate government interest. The government interest is (1) the avoidance of extraordinary rents to companies and their employees who are being subsidized by the government in order to keep the financial system working properly; and (2) preventing improper incentives and moral hazard in subsidized companies and their employees. Even if the tax is not well designed to achieve these goals, in the sense that other alternatives might achieve the government's purposes better, the tax substantially furthers these purposes.
There is no problem under the takings clause of the Fifth Amendment. The tax does not involve the seizure of real property or an interest in real property. The tax is regulatory and for a public purpose as stated above. Such a tax may or may not be good policy but it does not constitute a taking.
There is no problem under the Ex Post Facto clause because the tax is not a criminal sanction.
There is no problem under the Contracts Clause because the Contracts Clause binds the states, and not the federal government.
Finally, there is no problem under the Bill of Attainder Clause because the tax does not single out specific individuals for punishment; in addition it is both prospective and retrospective in application. First, the tax defines the class to which it applies to an abstractly defined group rather than naming particular individuals. It applies to persons working for enterprises that have received emergency government subsidy; it is not aimed at particular companies or specific employees. Second, the tax is for a regulatory purpose, as described above, and not for a punitive purpose. Preventing misuse of government funds, limiting bad incentives, and avoiding moral hazard are regulatory purposes, not punitive purposes. The fact that isolated members of Congress may have expressed an impermissible punitive or retributive purpose does not mean that the tax violates the Constitution if the text of the bill on its face has an overtly regulatory purpose. Third, the tax is both prospective and retrospective in its targets, which is consistent with a regulatory as opposed to a punitive purpose.
It is worth noting that the fact that the proposed taxes are constitutional does not mean that they are necessarily good public policy.