The Republican National Committee, which counts on unlimited "soft money" donations to run political campaigns, filed suit on Tuesday to overturn the ban on such donations, signed into law in March by President Bush.

The campaign finance reform law is being challenged by several groups, who say the ban is a violation of free speech rights for political groups like the RNC and the Democratic National Committee, which also relies on the large-size checks unabashedly collected from corporations, unions and others. 

The National Rifle Association, the AFL-CIO, the U.S. Chamber of Commerce, the National Association of Broadcasters and Sen. Mitch McConnell, R-Ky., have all filed suit charging the new law's restrictions on political ads during election periods is unconstitutional, as is the ban on soft money used to pay for overhead, issue ads and generic get-out-the-vote activities.

"When Republicans face unconstitutional obstructions of political activity, the RNC is obligated to protect and defend the equal access of all Americans to engage in protected political speech," RNC Chairman Marc Racicot said in a written statement.

The suit argues that the new law is overly vague, potentially chilling free speech and association as political parties try to figure out what they must do to comply with it.

Congress passed the finance laws — scheduled to take effect after the November election — the largest overhaul since the post-Watergate era. The bill had been proposed several times over the last seven years, and earned a presidential signature despite President Bush saying that it was flawed.

Bush was not consulted by the RNC before the suit was filed, said RNC spokesman Jim Dyke.

Tuesday was the last day challengers could file lawsuits on a "fast track" to the U.S. Supreme Court, which will have the final say on the law's constitutionality.

One coalition representing low-income voters filed suit saying the increase in limits on "hard money" — cash donations that are limited in size but go directly to candidates to be spent on any activity — is unconstitutional because it discriminates against non-wealthy voters.

U.S. Public Interest Research Group, the National Voting Rights Institute and ACORN, an advocacy group for low-income voters, filed suit Tuesday arguing that increasing the hard money limits gives wealthy voters and candidates undue political influence.

The Associated Press contributed to this report.