Representatives for ACORN sued the federal government Thursday morning in an attempt to regain the millions of dollars in funding the community organizing group lost after filmmakers videotaped its workers offering advice on how to commit tax fraud and various other felonies.

The suit charges Congress with violating the Constitution when it passed legislation in September that specifically targeted ACORN to lose federal housing, education and transportation funds.

That qualifies the legislation as bills of attainder, according to the Center for Constitutional Rights, which filed the suit on behalf of ACORN. A bill of attainder punishes a person or group without the benefit of a trial, and is illegal under Article 1 of the Constitution.

Bills of attainder have traditionally been understood to have more serious legal consequences -- including the seizure of private property and even capital punishment -- than Congress' decision to withhold funds that are at its discretion to disseminate. Though members of Congress have accused ACORN of corruption, it is not clear how the exercise of its own prerogative is outside the bounds of legislative power.

Critics of the group in Congress blasted the lawsuit as a last-ditch effort to save the foundering organization's bottom line.

"ACORN's baseless lawsuit is the first public acknowledgement we've seen from ACORN of just how desperate they are to use any mechanism available to subsidize an organization that is teetering on bankruptcy and financial insolvency," said Kurt Bardella, spokesman for Rep. Darrell Issa, R-Calif.

Congress began cracking down on its funding to ACORN after its employees were secretly videotaped in a number of cities offering to help a man and woman posing as a pimp and prostitute to lie to the IRS and acquire illegal home loans.

Footage showed staffers advising the "pimp" and "prostitute" on how to falsify tax forms and seek illegal benefits for 13 "very young" girls from El Salvador that the pair said they wanted to bring to the country to work as child prostitutes. The videos set off a firestorm in Congress.

ACORN pledged an internal inquiry and fired the staffers who were caught on tape, but it was only the latest of many legal troubles for the Association of Community Organizations for Reform Now.

State investigators raided ACORN offices in Louisiana last week, seizing computer hard drives and documents in a probe of alleged embezzlement and tax fraud. Staffers in multiple states have been accused of committing voter registration fraud.

Congress took the "prostitute" videos as clear evidence of systematic problems within ACORN and voted with bipartisan support in the House and Senate to freeze funding for the group in appropriations bills in September.

Thursday's lawsuit claims that Congress violated the right to due process enshrined in the Fifth Amendment -- declaring the group guilty of a crime and punishing its members without completing an investigation within the Department of Justice or the IRS.

"It's not the job of Congress to be the judge, jury, and executioner," said Jules Lobel, an attorney representing the Center for Constitutional Rights.

"We have due process in this country, and our Constitution forbids lawmakers from singling out a person or group for punishment without a fair investigation and trial."

The lawsuit itself singles out three defendants -- Treasury Secretary Timothy Geithner; Director of the Office of Management and the Budget Peter Orszag, and Housing and Urban Development Secretary Shaun Donovan.

The three were responsible for facilitating the defunding of ACORN by Congress, according to attorneys for the Center for Constitutional Rights.

ACORN claims it has been badly hurt by the congressional actions, and has had to fire workers and close some of its 1,200 branches around the country.

Though it remains unclear precisely how much money the national organization was receiving from federal sources and aid programs, a lawyer pressing the suit said ACORN has already lost an amount "in the millions" since the freeze took effect.