Nader's lawsuit, filed in District of Columbia Superior Court, also named as co-defendants Kerry's campaign, the Service Employees International Union and several so-called 527 organizations such as America Coming Together, which were created to promote voter turnout on behalf of the Democratic ticket.
The lawsuit also alleges that the Democratic National Committee conspired to force Nader off the ballot in several states.
"The Democratic Party is going after anyone who presents a credible challenge to their monopoly over their perceived voters," Nader said in a statement. "This lawsuit was filed to help advance a free and open electoral process for all candidates and voters. Candidate rights and voter rights nourish each other for more voices, choices, and a more open and competitive democracy."
Among other things, the lawsuit alleges that the DNC tried to bankrupt Nader's campaign by suing to keep him off the ballot in 18 states. It also suggests the DNC sent Kerry supporters to crash a Nader petition drive in Portland, Ore., in June 2004, preventing him from collecting enough signatures to get on the ballot.
The lawsuit seeks "compensatory damages, punitive damages and injunctive relief to enjoin the defendants from ongoing and future violations of the law."
Nader's attorney, Bruce Afran, argued that the DNC would be terrified of having the case come to trial. He said he hoped the committee would choose to settle the case and apologize.
"This is a case designed to make sure other independent and third party candidates will not be subject to the same kind of conspiracy in the future," Afran said.
Nader received 463,653 votes in the election, or 0.38% of total votes cast.
DNC spokesman Luis Miranda declined comment on the suit, citing a policy on pending litigation.