The legal fight in Pennsylvania over mail-in ballots with missing or incorrect dates could drag on for weeks after Election Day, forcing courts to make the final decision on whether thousands of votes can be counted.

The battle is playing out in both in state and federal court against the backdrop of a very close U.S. Senate race that may decide control of the upper chamber. On one side are Democrat officials and activist groups who want to allow mail-in votes to count despite "minor errors." On the other are state, local and national Republican committees insisting on strict adherence to state law on how to fill out these ballots.

"Past experience tells us these kinds of things can drag on for what seems like an eternity," Pennsylvania Republican Party general counsel Tom King told Fox News Digital.

"What we have going on is a mad scramble as we speak," King added.

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The most high-profile ongoing litigation is a federal lawsuit from the NAACP and other groups – represented by the ACLU – that seeks to force officials to count mail ballots with incorrect or missing dates, despite a Pennsylvania Supreme Court ruling mandating they be sequestered. Democratic U.S. Senate candidate and Lt. Gov. John Fetterman, who is running against Republican Mehmet Oz, later filed a similar federal suit.

Information already released by major metropolitan areas indicates the number of ballots that fall into those categories could be significant. Allegheny County, where Pittsburgh is located, and Philadelphia County released lists of voters with date-related issues on their ballots, aiming to give those voters a chance to fix them. In Philadelphia, the number was over 2,300, and in Allegheny County it was about 1,000.

Those two counties make up just over one-fifth of Pennsylvania's population. Assuming similar rates of ballot issues elsewhere, the total number of deficient ballots could potentially exceed 10,000 and approach 15,000 or more.

ACLU lawyers argue that disqualifying votes based on "minor errors" like incorrect or missing dates runs afoul of the Civil Rights Act. The law, they say, makes it illegal not to count votes based on paperwork mistakes "not material" to whether a voter is eligible.

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"There's a certain amount of common sense here that should say these votes should count," R Street Institute resident elections fellow Matthew Germer told Fox News Digital. "If a ballot arrives in advance of Election Day, it's pretty clear to me at least that that ballot should be counted."

Germer said it is possible court cases related to Pennsylvania's elections continue for days or weeks after Election Day, and could potentially make it to the Supreme Court. However, he argued, that is not necessarily a bad thing – and that it is likely the courts will come to a conclusion well before the results legally must be certified.

"I would expect the first kind of ruling within a week. And then if there are any appeals that move forward from there, that it jumps to the top of the docket for almost any court that's going to be handling it," Germer said.

Germer also noted that if the state's U.S. Senate race between Fetterman and Oz is not close, the sequestered mail ballots may not matter at all.

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Meanwhile, Pennsylvania Acting Secretary of State Leigh Chapman is asking counties to go through mail-in ballots and report to the state how many had missing or incorrect dates. She also says she wants counties reach out to and help voters who made mistakes to fix them.

"It is the Department of State's position that voters who make, you know, minor errors on their ballot – if they forget to sign it, if they forget to date it – you know, they should be able to go to their county, fix that issue," Chapman said Monday.

However, Republicans argue that scheme violates state law, which they say requires mail ballots to be stored in secure locations until official are allowed to start processing them at 7 a.m. on Election Day. The Monroe County GOP, with backing from King, sued the Monroe County Board of Elections over that last week.

A judge Monday ruled against a GOP request for a preliminary injunction against the county. He said where election law is unclear, it should be interpreted in a way that avoids disenfranchising people.

"Given that our Supreme Court's policy has been to enfranchise the voter when interpreting ambiguous statutes… I find that MCRC has not shown a strong likelihood of success at this very early stage of litigation," wrote Monroe County Court of Common Pleas Judge Arthur L. Zulick.

King said after the ruling came down that the GOP would wait until after election results come in before deciding how to move forward on that legal issue. He said it is "a basis upon which to challenge votes if it's appropriate."

"In the event of close elections, there will be numerous challenges across the state of Pennsylvania to any of these ballots that were processed in this way," King said.

Fox News' Courtney De George contributed to this report.