The Republican National Committee is intervening against the David McCormick campaign's lawsuit attempting to force the counting of undated absentee ballots in Pennsylvania's Senate primary, as his opponent, celebrity heart surgeon Dr. Mehmet Oz, leads by a tiny fraction of a percent. 

An RNC official confirmed reports about the intervention to Fox News Digital Monday night, insisting that the move does not signal support for Oz or opposition to McCormick but rather an attempt to preserve election integrity.

"The RNC is intervening in this lawsuit alongside the Pennsylvania GOP because election laws are meant to be followed, and changing the rules when ballots are already being counted harms the integrity of our elections," RNC chief counsel Matt Raymer said in a statement. 

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Dr. Mehmet Oz and David McCormick (Getty Images)

"Either of Pennsylvania’s leading Republican Senate candidates would represent the Keystone State better than a Democrat, but Pennsylvania law is clear that undated absentee ballots may not be counted," Raymer added. "This is another example of the RNC’s ironclad commitment to ensuring that the highest standards of transparency and security are upheld throughout the election process."

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The Pennsylvania GOP also condemned the move. "While the Republican Party of Pennsylvania looks forward to supporting the Pennsylvania Republican U.S. Senate nominee, whoever it may be, we absolutely object ot the counting of undated mail-in ballots," the party said in a statement. "Pennsylvania law and our courts have been very clear that undated ballots are not to be counted."

McCormick's campaign filed the lawsuit in a Pennsylvania court after-hours on Monday, aiming to ensure that counties obey a federal appeals court decision asking the state's Commonwealth Court to require counties to promptly count mail-in ballots that lack the required handwritten date on the return envelope.

David McCormick

Dave McCormick shakes hands with supporters at a rally to raise support for his Senate bid. (Aimee Dilger/SOPA Images/LightRocket via Getty Images)

In the lawsuit, McCormick's campaign claimed that at least two counties – Blair and Allegheny – suggested they would not count the ballots as part of their unofficial result that each county must report to the state on Tuesday. 

"Both the Pennsylvania Supreme Court and the United States Court of Appeals for the Third Circuit have held that mail-in ballots should not be disqualified simply because the voters failed to hand write a date on the exterior mailing envelope of their ballots," Chuck Cooper, chief legal counsel for McCormick's campaign, told Fox News Digital Tuesday. "Because all ballots are time stamped by the County Boards of Elections on receipt, a voter's handwritten date is meaningless.  All timely ballots of qualified Republican voters should be counted."

A McCormick source said that the litigation aims to compel the counties to follow a Friday ruling from the 3rd U.S. Circuit Court of Appeals, which ruled that the requirement is "immaterial" because counties nonetheless can verify that the ballots have been returned on time, due to the postmark.

As of 6 p.m. Monday, Oz, whom former President Donald Trump endorsed, led McCormick by 992 votes (0.07%) out of 1,341,037 ballots. The race is likely close enough to trigger Pennsylvania's automatic recount law, which applies inside the law's 0.5% margin. 

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The number of mail-in ballots lacking a handwritten note remains unclear. While McCormick, a former hedge fund CEO and former George W. Bush administration Treasury official, trails in the overall vote, he has been outperforming Oz in mail-in ballots.

McCormick said that "every Republican vote should count" in an appearance on a conservative Philadelphia talk show Monday. 

"The premise we should have, I believe, as Republicans is that all Republican votes count, and that’s something we’ve all, I think, held as a principle," McCormick said. "And so that’s the principle we’re holding here. We held that principle before this court ruling. This court ruling just illuminated it more."

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Senate candidate Mehmet Oz, accompanied by former President Donald Trump, speaks at a campaign rally in Greensburg, Pennsylvania, May 6, 2022. (AP Photo/Gene J. Puskar)

Casey Contres, Oz's campaign manager, condemned McCormick's legal team in a statement Saturday.

Contres noted that McCormick "is likely going to come up short" and claimed that "the McCormick legal team is following the Democrats' playbook, a tactic that could have long-term harmful consequences for elections in the Commonwealth of Pennsylvania."

"Dr. Mehmet Oz continues to respectfully allow Pennsylvania's vote-counting process to take place and puts his faith in the Republican voters who we believe have chosen him as their nominee," Contres added. "That is why our campaign will oppose the McCormick legal team's request that election boards ignore both Pennsylvania's Supreme Court and state election law and accept legally rejected ballots." 

Yet a McCormick spokesperson told Fox News Digital that Oz's campaign filed a legal motion for a "global challenge to Republican voters" against ballots that were not signed in Philadelphia County. The spokesperson said that "while the McCormick campaign is fighting to ensure every valid Republican vote is counted," Oz's team is "fighting to disenfranchise Republican voters."

Democratic lawyer Marc Elias, who represented the Hillary Clinton campaign in 2016 and who pushed a multi-state challenge against voter identification laws, appeared to champion McCormick's cause.

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"My team was literally working on this same lawsuit for the November election," Elias said on Twitter.

The Associated Press contributed to this report.