Sen. Bill Nelson Clarence (Bill) William NelsonDemocrats sound alarm on possible election chaos Trump, facing trouble in Florida, goes all in NASA names DC headquarters after agency's first Black female engineer Mary W. Jackson MORE's (D-Fla.) campaign filed a lawsuit on Tuesday seeking to bar Florida's top elections official from rejecting unconventionally marked ballots.

The lawsuit, filed in federal court by both Nelson and the Senate Democrats' campaign arm in Tallahassee, asks a judge to ensure that the Florida Department of State does not disqualify ballots where selections are marked in different ways, so long as the voter's intention is clear.

A ruling in the lawsuit could be key in determining whether numerous ballots are tallied if the Senate race in Florida goes to a hand recount.

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The lawsuit argues that Florida Secretary of State Ken Detzner's office could reject ballots on which a voter may have marked a selection in more than one way.

Such ballots may appear as overvotes or undervotes — ballots on which a voters' selections either exceed or fall below the maximum number of selections allowed — in vote-counting machines and therefore may have been overlooked by county election officials.

The Nelson campaign's lawsuit asks a judge to ensure that such ballots are counted should the Senate race go to a hand recount.

"The State will incur no burden in counting the votes of voters who clearly indicated their definite choice for Florida’s U.S. Senate race, but may not have done so in the same manner for every race on the ballot or may not have cancelled-out erroneous overvotes using written words ...," the lawsuit reads.

Nelson is locked in a heated fight to the finish against Florida's Republican Gov. Rick Scott in the Senate race as county election officials scramble to meet a key Thursday deadline to complete a machine recount.

As early vote returns came in on Election Day, Scott appeared on track for a victory. But as more vote tallies ticked in throughout the rest of the week, his lead narrowed considerably, forcing the race into a recount.

The latest vote count shows Nelson and Scott separated by less than 13,000 votes — or about 0.15 percentage points.

In Florida, a machine recount is triggered when two candidates are 0.5 points apart or less. If 0.25 points or less separate the candidates after the machine recount, a manual recount takes effect.

Marc Elias, the lead elections lawyer for Nelson, has said that the senator is likely to benefit from a hand recount, because some of the disputed ballots might be added to his total.

Meanwhile, Scott and Republicans have raised the prospect of elections fraud, particularly in Democrat-heavy South Florida, though they have provided no evidence to back up those claims.

The Florida Department of Law Enforcement and the Department of State have said that they have not received any credible allegations of fraud or criminal activity.

The recount has spurred a flurry of legal activity from both sides of the aisle. A lawsuit from the Nelson campaign regarding how election officials evaluate provisional ballots is set to go back to court on Wednesday.