Sen. Mitch McConnell, R-Ky., and the National Rifle Association had brought suits claiming the campaign finance reform act violates free speech protections. The new law bars political parties from collecting unregulated donations and limits some advertising by outside groups in the days immediately prior an election.
Senate sponsors John McCain, R-Ariz., Russ Feingold, D-Wis., Olympia Snowe, R-Maine, and Jim Jeffords, I-Vt., joined House sponsors Chris Shays, R-Conn., and Marty Meehan, D-Mass., in a motion to intervene in the lawsuits against the new law.
The case will be heard in U.S. District Court in Washington.
Opponents claim that limiting fundraising and political advertising is tantamount to a limit on political speech, which is protected by the U.S. Constitution. McCain disagreed with that assessment and said the law will protect the political system established by the Constitution.
"We are intervening today in the NRA and McConnell cases to defend the constitutionality of all aspects of the new campaign finance law," he said.
The filing itself states that the challenge to the law is unfounded.
"The sponsors will show that the provisions challenged by the plaintiff are constitutional, and that the act affirmatively promotes and enhances core First Amendment values," the filing says. "As the legislative record reflects, the American electorate is losing confidence in the democratic process because of the specter of actual and apparent corruption created by 'soft money' and other campaign finance abuses, and because of the climate of evasion of legitimate regulation that has come to characterize our political system."
McConnell and the NRA both filed separate lawsuits on March 27, but it is expected that the challenges to the new law, which could also come from civil liberties organizations, might be joined into a single suit at a later date.
"I filed suit to defend the First Amendment right of all Americans to be able to fully participate in the political process," McConnell said at the time of suit. "I look forward to being joined by a strong group of co-plaintiffs in the very near future."