Top Republicans in the Pennsylvania legislature threatened Friday to impeach Philadelphia elections officials if they count undated mail ballots from last week’s primary, a major escalation in ongoing legal and political fights over how elections are run.

Four of the seven justices on the Pennsylvania Supreme Court said in a decision last year that voters must sign and date envelopes when returning mail ballots. Republicans pointed to that case, saying counties must reject the undated ballots. In a letter to city commissioners Lisa Deeley and Omar Sabir, the two Democrats who voted this week to count them, the lawmakers demanded they “immediately rescind your endorsement of this unlawful action.”

“So there can be no misunderstanding — failure to promptly conform to Pennsylvania law will leave us no choice but to seek your removal from office using the authority vested to the House of Representatives,” the legislative leaders wrote.

It’s extremely rare to impeach elected officials and attempt to remove them from office. Any lawmakers can introduce impeachment resolutions — just this month, three lawmakers tried to launch an impeachment probe of a Schuylkill County commissioner. Such efforts usually go nowhere.

Top legislative leaders publicly threatening impeachment is an extraordinary move likely to further inflame partisan conflict and the voting wars that have taken center stage in Harrisburg and elsewhere since the 2020 election and the false claims of widespread fraud that followed it.

The letters were signed by state House Speaker Bryan Cutler (R., Lancaster); seven Republican House leaders, including Majority Leader Kerry Benninghoff (R., Centre) and Rep. Martina White, the head of the Philadelphia GOP; and Rep. Seth Grove (R., York), the chair of the House State Government Committee and lead lawmaker handling election issues.

» READ MORE: Philly will count undated mail ballots the Pa. Supreme Court said should be thrown out

In a 2-1 vote Wednesday, Deeley and Sabir voted to count the undated ballots, while Republican commissioner Al Schmidt voted to reject them. Schmidt said the law and the court ruling required him to do so. There were 1,319 undated Philadelphia mail ballots for the May 18 primary, about 2% of the 64,000 ballots received by the deadline that night. Counting them isn’t expected to change the outcome of any races.

Officials in Bucks, Chester, Delaware, and Montgomery Counties said they are also counting undated mail ballots.

“It is unbecoming of the House Republican leaders to try and extort another elected official to change their vote,” Deeley said in a statement. “There is a formal process of appealing decisions from Boards of Elections that is prescribed in the Election Code, and we have yet to receive any appeal — nor am I aware of an appeal in any county.

“Really this is nothing more than yet another effort to grandstand and sow doubt in the electoral process while scoring political points at Philadelphia’s expense,” she added. “Instead of working to address an issue that could disenfranchise over 1,300 Philadelphians they are playing games.”

Sabir also defended his decision.

“I took an oath to protect the right for people to vote,” he said. “Many people fought and died to ensure people had a right to vote, and my stance aligns with that.”

Impeachment formally accuses an elected official of a crime or other misconduct, and the Pennsylvania state constitution lays out a process similar to how it works in Congress. The state House can introduce articles of impeachment that are then passed by a simple majority vote. The state Senate then holds a trial requiring a two-thirds majority to convict, which can result in removing someone from office and preventing them from holding future office.

Republicans in Harrisburg control both chambers and would have enough votes to impeach if their caucus remained unified, but would unlikely be able to muster the supermajority needed to remove Deeley and Sabir from office.

» READ MORE: The Pennsylvania primary showed that running elections is complicated — and so is changing election law

While other counties are also counting the undated ballots, Republicans’ focus is currently on Philadelphia, according to a person familiar with lawmakers’ discussions who spoke on condition of anonymity. “Hopefully that sends a message to the rest of the counties,” this person said.

A spokesperson for House Republicans declined to comment beyond the letter.

“It’s troubling that the same House Republicans who demanded Congress refuse to count millions of Pennsylvania’s ballots last November are now threatening Philadelphia’s election commissioners for counting citizen ballots legally cast in the primary,” state Rep. Joanna McClinton (D., Philadelphia), the Democratic leader, said in a statement. “We need to focus on making it easier, simpler, and more convenient for everyone to vote, and stop these partisan games.

Philadelphia officials plan to open and count the undated ballots Saturday and include those results in the official vote count, but the undated ballots will remain physically separated from others.

The state Supreme Court ruled in November that undated ballots be counted for the 2020 election. Three justices interpreted state election law to always allow counting undated ballots, while three justices said the law didn’t allow it. The seventh, Justice David Wecht, was the deciding vote, saying undated ballots should be counted in 2020 but rejected in the future — once voters had better instructions about dating ballots and the consequences for failing to do so.

Last year was the first in which any Pennsylvania voter could cast a mail ballot.

Election lawyers in both parties agreed the decision meant unsigned or undated ballots should be thrown out in future elections. But Adam Bonin, a Democratic election lawyer in Philadelphia, said this week that it left room for interpretation because the large number of undated ballots could suggest voters didn’t have the “adequate instructions” and “sufficient warnings” that Wecht expected.

Matt Haverstick, a Republican election lawyer, disagreed, saying the bottom line is that four justices agreed mail ballots need dates to count.

“It’s flagrantly wrong, it’s a clear violation of the law,” Haverstick said. “There’s no viable legal argument I can think of to get around the fact that four justices believe ... that ballots without dates don’t count.”