Several former third-party presidential hopefuls filed a lawsuit Wednesday to block the Commission on Presidential Debates from sponsoring future debates, claiming the organization is biased toward the Democratic and Republican parties.

The lawsuit, filed in federal court, claims the debate commission is a partisan organization that violates federal election law by letting only Democratic and Republican candidates participate in the debates it organizes.

Those filing Wednesday's lawsuit include consumer advocate Ralph Nader (search), the Green Party's presidential nominee in 2000 and a possible independent candidate this year; John Hagelin and Patrick Buchanan (search), former Reform Party candidates; and Howard Phillips (search), a former Constitution Party candidate.

The lawsuit asks the court to force the Federal Election Commission (search) to stop the debate commission from sponsoring four national debates scheduled to start on Sept. 30 in Miami. The third-party candidates first sought relief from the FEC last June, but complain that the agency has failed to take action.

FEC spokesman Bob Biersack said he could not comment on pending litigation.

Janet Brown, executive director of the debate commission, said the lawsuit rehashes many of the same claims that courts rejected before the last round of presidential debates.

Founded in 1987, the debate commission is a nonprofit corporation that allows candidates with at least 15 percent support in national polls to participate in its debates. Minor-party candidates have long complained that they are unfairly excluded, but the commission says it wants to limit participation to those candidates with a realistic chance of winning the election.

The lawsuit also alleges that the commission excluded the plaintiffs from even sitting in the audience at the debates in 2000, and that it distributed a 'face book' of prominent third-party candidates at one debate so staff could recognize and deny them access to the debate hall even if they had a ticket.

The candidates also want the FEC to order the commission to return millions of dollars raised from corporations and others to stage the 2000 debates, calling the money an illegal corporate contribution to the major parties.