HARRISBURG, Pa. (AP) — Pennsylvania's top election official has asked the state's highest court to back her up in a new legal dispute with President Donald Trump's campaign over whether counties should count mail-in ballots when a voter's signature doesn’t necessarily match the one on their registration.

The filing, at midnight Sunday by Secretary of State Kathy Boockvar, a Democrat, comes several days after Trump's campaign raised the matter in its wider, election-related federal court case in the presidential battleground state.

In guidance last month to counties, Boockvar told them that state law does not require or permit them to reject a mail-in ballot solely over a perceived signature inconsistency.

In her court filing, Boockvar asked the state Supreme Court to make that clear, and make it clear that a third party — like a presidential campaign or political party — is not permitted by the law to challenge ballots based on their signature analysis.

Such rejections poses “a grave risk of disenfranchisement on an arbitrary and wholly subjective basis,” Boockvar's filing said, and without any opportunity for a voter to answer questions about the signature before the ballot could be thrown out.

Her guidance to counties comes amid a surge in mail-in voting and rising concerns that tens of thousands of mail-in ballots will be discarded in the presidential election over a variety of technicalities.

The fight over signatures is one of many partisan battles being fought in the state Legislature and the courts over mail-in voting in Pennsylvania, amid concerns that a presidential election result will hang in limbo for days on a drawn-out vote count in Pennsylvania.

County election officials say people’s signatures change over time, with age or medical conditions. They also say questions about whether a voter's signature is valid have historically been extremely rare and, because of that, there has never before been a debate about it.

“It was really low on the list of concerns for mail ballots, absolutely,” said Jeff Greenburg, the former Mercer County elections director who now works for the National Vote at Home Institute. “I don’t have a number, but I would venture to say that the number of ballots turned away due to a signature question was slim to none. I'm sure it wasn’t none, but it was infinitesimal.”

But in the Nov. 3 presidential election, Pennsylvania is bracing to receive more than 3 million mail-in ballots, many of them from people who have never voted by mail before. That figure is more than 10 times the number of mail-in received in 2016's presidential election, fueled by a year-old law vastly expanding mail-in voting and concerns over voting in person during the pandemic.

In federal court, Trump's campaign has asked a judge to declare that Boockvar's guidance is unconstitutional and to block counties from following that guidance.

The Trump campaign argues that the law is clear that election officials must compare the information on the mail-in ballot envelope, including a voter's signature, to a voter's information on file to determine a person's qualifications to vote.

“The mandatory language of these provisions makes clear that the consequence of a failure to verify a voter’s qualification through signature comparison is the denial of that application and the setting aside of that elector’s voted ballot,” the Trump campaign wrote in its filing Tuesday in federal court.

The judge in that case may rule any day.

In that case, Trump's campaign is also trying to remove a county residency requirement on certified poll watchers and ban counties from using drop boxes or mobile sites to collect mail-in ballots that are not “staffed, secured, and employed consistently within and across all 67 of Pennsylvania’s counties.”

Trump’s campaign is also suing Philadelphia over city officials preventing campaign representatives from watching people registering to vote or filling out mail-in ballots in election offices there, while state Republican lawmakers have asked the U.S. Supreme Court to block on a ruling in the state's court that extends the deadline in November’s election to receive and count mailed-in ballots.

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Follow Marc Levy on Twitter at www.twitter.com/timelywriter.

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AP’s Advance Voting guide brings you the facts about voting early, by mail or absentee from each state: https://interactives.ap.org/advance-voting-2020/