With the U.S. Senate seat hanging in the balance, the Yuma, Navajo, Apache and Maricopa County Republican parties filed a lawsuit against all Arizona county recorders and the Secretary of State late Wednesday.

A telephone hearing was scheduled for 11:15 a.m. Thursday in Maricopa County Superior Court.

The Republican groups are challenging the way counties verify signatures on mail-in ballots that are dropped off at the polls on Election Day, according to the complaint obtained by The Arizona Republic.

At stake is an unknown number of ballots that could tip the result of the U.S. Senate race. Just 17,000 votes separated Republican Martha McSally and Democrat Kyrsten Sinema as of Wednesday evening, a cliffhanger that could take days, if not weeks, to call.

The lawsuit seemed to signal Republicans' anxiety over Thursday's expected posting of additional results from Maricopa County, the most populous area of the state, where Sinema has dominated so far.

Rules for checking signatures

If there is a mismatch between the signature on file and the signature on an early ballot dropped off on Election Day, some county recorders — including Maricopa County Recorder Adrian Fontes — believe they can contact those voters after Election Day. In phone calls, they allow voters to verify that they did, in fact, sign the green envelope of the ballot, as required by law.

The lawsuit alleges that state law only allows this practice prior to Election Day, not after. It asserts the process is unfair to voters residing in other counties where that process is only allowed before Election Day.

The lawsuit asks the court to require all of the counties to implement uniform deadlines for ballot rehabilitation.

“A foundational principle of American democracy and our justice system is that all votes are treated equally,” Arizona Republican Party Chairman Jonathan Lines said in a statement to the newspaper.

"This equal protection under the law is enshrined in our Constitution. It is not fair nor just that voters in one county are treated differently under the law from other voters in Arizona. This suit seeks immediate redress of any inequality between ballots cast across Arizona. We stand behind our local county parties demand for equal treatment.”

Fontes, a Democrat, who just a week ago decided to allow voters to verify signatures after Election Day, said other counties, including Pima County, have been allowing this for years.

"There are voters all over Arizona that have been benefiting from (this practice) for over a decade and Maricopa County voters should have that same benefit of due process," Fontes said.

Fontes said he had not seen a copy of the lawsuit as of 6:30 p.m. Wednesday.

Brett Johnson, attorney for the Republicans, said Thursday before the hearing that Democrats were misconstruing the intent of the complaint. He said it is intended to ensure all votes are treated equally. He said the GOP parties want consistency among all counties when handling the mismatched-signature verification process.

"Our intent was never to suppress," Johnson told The Republic. "Our intent was to ensure all counties to follow the law. Because of what Maricopa and Pima have done, it is essential that all counties get the same benefits."

Democratic leaders challenge lawsuit

Felecia Rotellini, chair of the Arizona Democratic Party, promised a fight if votes are discounted.

"The Republican party is doing everything it can to silence thousands of Arizonans who already cast their ballots," she said in a prepared statement. "That's absolutely wrong, and the Arizona Democratic Party is fully prepared to fight to ensure that every last Arizonan has their vote counted."

Andy Gordon, an election-law attorney who represents Democrats, said the lawsuit is without merit. The arguments contained in the lawsuit were characterized to him by a person familiar with it, he said.

"It's classic Republican 11th-hour stuff," he said. "There are counties all over the state who have been doing this forever … and so now that we’ve got a different regime down here in Maricopa County, and we’ve got a really, really, really tight Senate race, suddenly the Republicans say, 'You shouldn’t’ be doing this, we need to call it off.'"

Gordon noted that aggrieved parties are required to act if issues arise: "You can’t sit on your hands until we see 'OK, now it’s close now we want to do something about it' "

Republicans defend the lawsuit

Lines, on behalf of the Arizona Republican Party, appeared to lay the groundwork for a legal complaint on Sunday.

He sent all county recorders a letter calling into question this process and separate emergency-voting processes in which some counties allowed voters to cast ballots over the weekend and on Monday.

Chris Herring, the Maricopa County Republicans chair, said it was his understanding that several county recorders were “treating ballots differently” when it came to the signature verification process.

“We just want all 15 counties treated the same way," he said.

Torunn Sinclair, a spokeswoman for McSally, declined to comment on the lawsuit.

James Owens, a spokesman for Sinema, did not immediately respondto requests for comment.

Republicans have not yet filed a lawsuit on the emergency voting issue.

Awaiting more results

Early results show McSally with a slight advantage. The next major results update isn't expected to come until 5 p.m. Thursday.

Neither candidate addressed supporters at election night watch parties.

McSally wrote on Twitter Wednesday evening that she felt good about the results so far.

"Gaining ground and feeling good," she wrote. "Thanks to everyone for the well wishes and kind words. We couldn't do this without our wingmen and wingwomen. We'll keep you updated."

Sinema wrote her own sentiments on Twitter Wednesday morning.

"This race is about you and we're going to make sure your vote is counted," she wrote. "There are a lot of outstanding ballots — especially those mailed-in — and a lot of reasons to feel good! We're doing the work & will keep you updated. Thanks for being on Team Sinema!"