A new lawsuit could unleash a late surge of multimillion-dollar contributions in this fall’s presidential race by allowing independent groups to use large gifts to run advertisements directly attacking and promoting candidates. A group seeking to unseat lawmakers who support strict campaign finance regulation, SpeechNow.org, filed a lawsuit yesterday to block the Federal Election Commission from enforcing the $5,000 limit that generally applies to an individual’s contribution to a political action committee.

The executive director of SpeechNow, David Keating, said the cap violates the First Amendment. He pointed to court rulings that individuals have the right to spend unlimited amounts on political ads as long as there is no coordination with candidates or their campaigns.

“Everyone agrees that one person can spend as much as he or she wants to say anything about any candidate. So why can’t two?” Mr. Keating asked at a news conference yesterday.

SpeechNow, represented by the Institute for Justice and the Center for Competitive Politics, is asking Judge James Robertson for a hearing within 20 days on the group’s request for a preliminary injunction. It is unclear how quickly the case will move, but it could be in front of a federal appeals court by spring or summer. The group’s central argument is that the usual justification for campaign finance laws, namely the desire to avoid real or apparent corruption, does not apply when individuals band together to speak while keeping a distance from any candidates.

“There’s no possible road to corruption under this structure,” Edward Crane, the president of the Cato Institute, who is involved with the group, said. SpeechNow’s rules call for immediate disclosure of all donations.

A law professor at the University of Virginia who has advised advocates of tighter campaign finance laws, Daniel Ortiz, said the promises such groups make about not coordinating with candidates are often illusory. “They actually tend to be run by people who are pretty much doppelgangers of the candidates or the parties,” the professor said. That makes the involvement of groups more prone to corruption than expenditures donors might make on their own, he said.

Mr. Ortiz said the lawsuit, which could end up at the Supreme Court, is a logical step for those seeking to undermine campaign finance laws. “It’s not a stupid move on their part, because the membership of the court has changed,” he said.

In 2004, more than $400 million flowed into the presidential race and other federal contests through so-called 527 organizations, named for a section of the tax code. Those groups ran ads about candidates but did not engage in the “express advocacy” planned by SpeechNow. The FEC launched investigations into many of the groups and donors that were active in 2004 and levied millions of dollars in penalties, which has left many donors wary of making similar gifts in 2008.

A Democratic campaign finance lawyer, Marc Elias, said a win by SpeechNow could lift that chill. “It would obviate some of the fear and risk that people have, but it might not completely solve the problem,” he said. However, the attorney said it was unclear whether the case would be resolved in time to impact this November’s election. “Political planning doesn’t happen on a dime,” he said.