The suit, filed Wednesday in Maricopa County Superior Court, alleges that Nader's petitions are invalid because the wrong name is listed as his candidate for vice president and more than 15,000 of the 21,000 names on petitions asking that Nader be put in the ballot are invalid.
Arizona Democratic Party Chairman Jim Pederson told the Washington Post the state group was not acting on behalf of the Democratic National Committee or the campaign of presumptive party candidate for president John Kerry.
Pederson told the Arizona Daily Star he was not contesting anyone's right to be on the ballot, but that it had to be "done in a legal and accurate way."
Nader told the Washington Post the Arizona suit is "potential harassment" and he threatened to concentrate his campaign "only on the close states."
The Nader campaign told the Arizona newspaper it believes the petition names are valid.