Well, it is likely unconstitutional. Congress may not write a bill to specifically punish a group. (Ever heard of a bill of attainder? It's where Congress writes a law that punishes one person or one group of people. This is not allowed under Article 1 of the US Constitution.)
However, if Congress decides to apply it broadly (meaning applying the law to all groups that do business with the gov't and not just single out ACORN) then it could get around the bill of attainder problem. Broadly applied the bill would apply to any organization accused of fraudulent interaction with a state or the federal government.
BUT that means other groups and corporations who receive government funding will be subject to the requirements laid out in the Act. Fair enough, right? Rules like this should be applied across the board! And, yes, it's best for the government not to give our hard-earned tax dollars to those who would defraud the government! Right?!
Well, THAT means certain other government-funded corporations will lose their government funding too - like Lockheed Martin which has been fined for government contract fraud 11 times. Lockheed Martin currently receives over 80% of its revenue from the U.S. government. Or the war contractor Blackwater which has also been caught committing government contract fraud. At least 90% of Blackwater's revenue comes from government contracts.
Watch the first 7 minutes of this clip to see more about why these & other corporations may lose their government funding.
Or read this. Or this.