The ballot for the Sept. 10 Democratic primary for governor instructs voters to "Vote for One Pair." It means they should choose a combined entry for governor and lieutenant governor.
But Democrats say that will be confusing because none of the gubernatorial candidates has chosen a running mate yet.
The suit is against the state and Florida's 67 county elections supervisors, aimed at changing the wording of the ballot.
Secretary of State Jim Smith has already instructed elections officials to determine whether it is possible to make any changes to the ballot before the primary, which is now five weeks away.