The U.S. Supreme Court injected fresh uncertainty Tuesday into the ongoing Republican primary recount for Pennsylvania’s U.S. Senate race by temporarily blocking a lower court order on the counting of undated mail ballots, which have become a flash point in the close contest between Mehmet Oz and David McCormick.

The two-sentence order — issued by Justice Samuel A. Alito Jr., who oversees emergency matters arising from Pennsylvania for the court — threw a new variable into the high-stakes contest by blocking undated ballots from being counted in an unrelated election from Lehigh County last November.

It came just hours after McCormick — who has pushed for undated ballots to be counted — appeared to make progress convincing the Pennsylvania Commonwealth Court to side with his view.

The new cloud of uncertainty came as more counties began recounting votes in the race.

Initial results show McCormick trailing Oz by fewer than 1,000 votes out of more than 1.3 million cast. The narrow margin has triggered an automatic recount to verify the winner, who will face Democratic Lt. Gov. John Fetterman in November. McCormick on Tuesday opened a new front in the court battles over which votes should count with a lawsuit seeking a hand recount of all ballots in 150 precincts in 12 Pennsylvania counties.

The immediate impact of Alito’s order on the Senate race remains to be seen. It focused solely on the counting of votes in a contested 2021 judicial race in Lehigh County. But much like the lower court ruling that prompted Alito’s intervention Tuesday, its repercussions could reverberate widely.

» READ MORE: U.S. Supreme Court injects new uncertainty into undated ballot counting; some counties have completed their recounts

At issue are mail ballots that arrived on time but are missing the handwritten date on their outer envelopes that is required by state law. Previously, those ballots would have been rejected.

But in ruling on the Lehigh County case in May, the U.S. Court of Appeals for the Third Circuit held that the state’s dating requirement — under which counties accept ballots with the wrong date as long as any date is on the envelope — was arbitrary in determining whether a ballot was cast by an eligible voter.

It ordered undated ballots to be included in the final tally of the Lehigh County race and said rejecting them for an immaterial technicality violates federal civil rights law.

McCormick has seized upon the ruling, arguing in Pennsylvania’s Commonwealth Court that the Third Circuit’s logic should apply to his race. He has generally outperformed Oz among mail voters.

Effects of Alito order on recount unclear

While Alito’s order Tuesday technically only pressed pause on counting undated ballots in the 2021 Lehigh County race while the wider Supreme Court decides whether it will hear an appeal, it could complicate the arguments McCormick made just hours earlier before Commonwealth Court President Judge Renee Cohn Jubelirer.

During the nearly four-hour proceeding in Harrisburg, Cohn Jubelirer appeared receptive at times to the Third Circuit’s conclusion that the way the state currently implements its dating requirement is arbitrary. After determining there are no allegations of fraud surrounding those votes in the McCormick-Oz race, she noted that the failure of eligible voters to date their ballots was most likely inadvertent.

“Have you ever made a mistake when you put a date on something?” she asked attorneys for Oz. “I know I have. … Should that defeat a person’s ability to vote?”

State elections officials, who have also come out in favor of counting mail ballots, maintained that it shouldn’t. But in an acknowledgment of the ongoing debate before various courts, they’ve advised counties for now to count their undated mail ballots, but keep those numbers separate from their overall vote tallies.

“We think the only real answer here is that these votes should be counted,” said Chief Deputy Attorney General Michael Fischer, arguing on behalf of acting Secretary of State Leigh M. Chapman. “If all the voter did was leave off an irrelevant date, then we should not disenfranchise them — and that’s what we’re talking about here, disenfranchisement.”

Attorneys for Oz — supported by both the state and national Republican parties — argued Tuesday that it would be just as unfair for a court to mandate the inclusion of ballots that would previously have been rejected while the counting process is still ongoing.

Describing McCormick’s legal push as part of a “broader effort to thwart the apparent will of Pennsylvania’s voters,” campaign attorney John Gore warned that any change to the rules after votes were cast risked undermining the public’s certainty in the final results.

“That’s not how we run elections, and that’s not a good way to run elections,” he said.

Cohn Jubelirer did not immediately rule on the matter at the conclusion of Tuesday’s hearing, saying only that she intended to make a decision “as quickly as possible.” It remains to be seen how much Alito’s order in the Lehigh County case could influence her.

Jess Szymanski, a spokesperson for the McCormick campaign, maintained it should have no bearing at all.

“The Commonwealth Court has every right to side with Republican voters throughout the commonwealth who cast a timely ballot on grounds rooted in the Pennsylvania constitution,” she said.

But Oz’s campaign has urged the judge to limit her ruling and suggested Tuesday that the court only weigh in if it becomes clear amid the ongoing recount that the undated ballot numbers are enough to help McCormick close his gap.

Recount proceeds across Pennsylvania

Meanwhile, across the state, the work of recounting all of the 1.3 million ballots cast in the race continued — a process that must be completed by June 7. The process is expected to be completed faster than the initial count, with many small counties able to finish within a day, and some larger ones taking several days.

Crawford, Montour, and Tioga Counties were among seven that began before the holiday weekend, and they completed their recounts in a matter of hours. Bedford County finished Monday morning.

Some results have shifted from the initial count, as expected, though in these smaller counties the differences were slight. McCormick picked up one vote in Bedford, one in Crawford, and one in Montour. Tioga’s recount didn’t change its initial results. Oz’s vote was unchanged in all four counties.

Philadelphia began its recount Sunday afternoon and was basically done Monday, with just a handful of votes waiting to be counted Tuesday evening, after a mandatory waiting period. When elections officials announced the final results of the initial tally and recount, they had also changed only very slightly: Oz gained one vote, and McCormick lost two of them. (The city’s vote counts included undated mail ballots, though it did separate them out in the numbers it sent to the state.)

Ballots are typically counted by machines in recounts. But in a new lawsuit Tuesday, McCormick’s campaign asked the Commonwealth Court to order hand recounts of ballots in 12 counties, pointing to discrepancies between vote tallies listed on county websites and those reported by the state.

» READ MORE: We don’t know the exact number of Oz and McCormick votes right now. Here’s why.

In their filing, the campaign homed in on precincts in each of the counties where they believe there are abnormalities, such as large discrepancies between the number of votes cast in the GOP gubernatorial and Senate primaries.

There’s no evidence of fraud in the count. Discrepancies in public tallies issued before results are finalized may result from several causes, including counties updating their websites at different times than they update the state.

The campaign’s lawsuit initially requested a hand recount in precincts in Allegheny, York, Centre, Chester, Cumberland, Erie, Lancaster, Monroe, Schuylkill, Delaware, Bucks, and Westmoreland Counties. It would run concurrently with the statewide recount, the campaign said.

“We understand that this process has already gone on too long. We’re all ready for it to be over with,” the official said. “It’s just the transparency. There’s an enormous lack of it.”

Staff writers Jonathan Tamari, Tyler Jenkins-Wong and Andrew Seidman contributed to this article.