(CNN) -- Democratic Sen. Bill Nelson's reelection campaign has filed a lawsuit against Florida Secretary of State Ken Detzner over vote-by-mail ballots and the process used to validate them.

RELATED: President hints at potential federal role in recount

Democratic lawyer Marc Elias, the lead recount lawyer for Nelson, decried the signature matching process that is used to validate provisional ballots, arguing that it leaves the decision to the "untrained opinions" of poll workers to determine "whether signatures match." He said there was a "complete lack of uniformity" in how those signatures were judged.

"This serves as an outright disenfranchisement and burden on the right to vote," Elias told reporter on a call Friday.

The lawsuit comes amid a bitter fight between Republicans and Democrats in the state over multiple electoral contests, including Nelson's race for reelection and the gubernatorial contest between Democrat Andrew Gillum and Republican Ron DeSantis. The Republican candidates' leads in both contests are narrowing as votes continue to be counted.

Democrats believe there are enough votes out to tip the Senate race towards Nelson, but are less confident in Gillum's race, where the divide is around 37,000 votes in DeSantis' favor.

Florida law mandates that any races within .5% would go to a machine recount. For those races that are within .25% after that machine recount, a hand recount would be initiated of ballots marked as undervotes (voters who did not fill out all available choices on the ballot) or overvotes (voters who made more choices than allotted on the ballot). The hand recount would only occur if there are enough overvotes, undervotes and provisional ballots left to change the outcome.

At the center of the battle is Detzner, a Republican who was appointed by Florida Gov. Rick Scott, Nelson's GOP opponent in the contested Senate race.

The lawsuit, brought by Nelson's campaign and the Democratic Executive Committee of Florida, asks for all votes cast using vote-by-mail or those "determined to involve a signature mismatch, be counted as valid votes."

"This entirely standardless, inconsistent, and unreliable signature matching process, which has a disparate impact on People of Color and young, first time voters, violates the prohibition against undue burdens on the right to vote, enshrined under the First and Fourteenth Amendments to the U.S. Constitution, and subjects Florida voters to disparate treatment and inconsistent standards in violation of the Fourteenth Amendment's Equal Protection Clause," reads the lawsuit.

Elias opened a call with reporters on Friday l by highlighting how the split between Scott and Nelson has shrunk since Election Day and confidently said he believed, after all votes are counted correctly, Nelson would prevail the winner.

"I would expect when we go into a machine recount and then a hand recount, right now the results are unknown who has won, and if I had to place a bet, I would say it is more likely than not Sen. Nelson will prevail in a recount," he said.

Elias dismissed suggestions that there are not enough votes out there to close the margin for Nelson.

"Fifteen thousand is a lot of votes when you are talking about an election of one million votes or two million votes. We are talking about 8.5 million votes. We are less than two-tenths of one percent. ... And when viewed in that arena, it is actually quite close."

Scott's campaign wasted no time in responding to Elias, charging in a statement that Nelson and his lawyers are conducting "fraud" in fighting the current results.

"Until today, the Nelson campaign has been working on voter fraud behind the scenes in secret," read the statement. "With today's filing, their desperation has driven them to ask the federal courts to allow voter fraud. They are asking courts to overrule election officials and accept ballots that were not legally cast."

They added: "Bill Nelson's entire campaign has been a fraud. Nelson relied on fraud when he attacked Gov. Rick Scott's record, Nelson relied on fraud when he misrepresented his Senate record, and now he is hoping that voter fraud will help him hang on to power."

In total, the statement used the word "fraud" six times.

The statement comes hours after Scott stepped outside the governor's mansion in Florida on Thursday night to announced that he and the National Republican Senatorial Committee were filing two lawsuits, one against Broward Supervisor of Elections Brenda C. Snipes and another against Palm Beach County Supervisor of Elections Susan Bucher.

"The people of Florida deserve fairness and transparency, and the supervisors are failing to give it to us," Scott said. "Every Floridian should be concerned there may be rampant fraud happening in Palm Beach and Broward counties."

The governor also went after Elias, listing all of the other recount elections he has been involved in and faulting him for telling reporters he was "here to win the election."

"He is here to try to steal the election, and to try to thwart the will of the voters of Florida," Scott said.

Elias responded on Friday, calling his list a "promotional video" for the lawyer.

"I thank him for that," the Democratic lawyer said dryly.

The fact that there will be multiple high-profile recounts in Florida gives many political watchers deja vu, given the impact that the state's recount played on the 2000 presidential election that saw President George W. Bush elected after winning Florida by 537 votes.

President Donald Trump also weighed in on the recount, attacking Elias as Democrats' "best Election stealing lawyer."

"As soon as Democrats sent their best Election stealing lawyer, Marc Elias, to Broward County they miraculously started finding Democrat votes," he said on Twitter. "Don't worry, Florida - I am sending much better lawyers to expose the FRAUD!"

A White House official and representatives from the Republican National Committee and NRSC did not respond to requests for comment about which lawyers Trump has dispatched to Florida.

The-CNN-Wire

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