Democrats in the Pennsylvania Senate sued their Republican colleagues Friday evening to block them from subpoenaing voter records as part of a review of the 2020 election.

The lawsuit argues that the Republican effort unconstitutionally tramples on the separation of powers by stepping on the courts’ power to investigate and rule on election disputes and on the executive branch’s power, given specifically to the state auditor general, to audit how elections are run. The lawsuit also contends that the subpoena violates state election law because it requests voters’ private information, including driver’s license numbers and the last four digits of Social Security numbers.

Senate Democrats “ask this Court to prevent violation of the Pennsylvania Election Code and the Pennsylvania Constitution through [Republican lawmakers’] untimely election contest and to protect the rights of the approximately 6.9 million Pennsylvanians who cast votes in the 2020 General Election, including protection from the unlawful disclosure of their private information” in the state voter database, the suit reads.

» READ MORE: Pa. Republicans vote to subpoena voter records and personal information in 2020 election probe

The lawsuit was filed by the Senate Democratic Caucus, headed by Democratic Leader Sen. Jay Costa (D., Allegheny), in Commonwealth Court, the state court that handles government issues. The defendants are Senate President Pro Tempore Jake Corman (R., Centre), the highest-ranking state senator and backer of the election review; Sen. Cris Dush (R., Jefferson), whom Corman assigned to lead the effort; and Megan Martin, the Senate’s secretary-parliamentarian.

In addition to asking the court to block Wednesday’s subpoena, Senate Democrats are attempting to stop the broader election review effort.

Jason Thompson, a spokesperson for Corman and Dush, declined to comment on the lawsuit itself. In a statement Saturday, he pushed back on Democrats’ security concerns around voter information.

“[I]t is disappointing the security issue has been sensationalized by Senate Democrats to the nth degree,” he said. The state legislature works with personal information “all the time ... and we have done so for many, many years without incident.”

He noted that both Corman and Dush have said that any third-party contractor given access to private information “will be required to meet the same high standards of information security under penalty of law.”

» READ MORE: Pa. Republicans are set to subpoena documents and hire a contractor for their 2020 election review

Friday’s lawsuit was the first court attempt by Democrats to stop what Republican senators call a “forensic investigation” or “forensic audit” of election administration and results. At the federal level, U.S. Rep. Mary Gay Scanlon, a Democrat in a district based in Delaware County, asked Friday for the Department of Justice’s Civil Rights Division to investigate the “authorization of a subpoena of breathtaking scope.”

Scanlon, the vice chair of the Committee on House Administration, wrote in a letter with Rep. Zoe Lofgren (D., Calif.), the chair of that committee, that the two are concerned about the subpoena and broad election review effort intimidating voters, including potentially deterring people from registering if they believe their personal information will not be protected.

Republicans say the effort to review the 2020 general and 2021 primary elections is necessary to address the concerns of their constituents and restore public confidence in the electoral system. (Much of the mistrust has been fueled by former President Donald Trump’s lies about voter fraud and stolen elections.)

Democrats say the effort, which officially began this month in the Republican-controlled state Senate, is a nakedly partisan attempt to overturn election results, further undermine confidence in elections, and appease the Trump base.

Trump for months called for an “audit” of election results in Pennsylvania, with supporters rallying behind State Sen. Doug Mastriano, a likely gubernatorial candidate who has spread false claims about the 2020 election and risen to political prominence by promising to investigate the election. Republican legislative leaders sought to resist those calls by emphasizing legislative reform, but the rift between wings of the party grew as pressure mounted.

Mastriano in July sent letters to Philadelphia, Tioga, and York Counties seeking virtually all election materials, equipment, and records, threatening to subpoena the counties if they didn’t comply. Philadelphia elections officials rejected the request, with Tioga and York officials also pushing back and not complying.

Mastriano’s attempt drew praise from supporters of the movement to investigate the election, but angered some Republicans who saw him as engaging in an unnecessary political exercise that would drag them into a protracted political and legal fight. Some Republicans worried that Mastriano’s aggressive rhetoric and actions would bring court scrutiny and that the result, especially if it went to the majority-Democrat state Supreme Court, would be restrictions on legislative subpoena powers.

Those tensions boiled over last month, when Corman brought the feud into public view, lashing out at Mastriano, reassigning his Capitol staff, and removing him as chair of the Senate Intergovernmental Operations Committee. At the same time, Corman for the first time fully backed a review of the 2020 election, naming Dush as committee chair and assigning him to pursue the review effort.

» READ MORE: The Pa. Senate leader resisted his pro-Trump wing for months. Now he wants a MAGA makeover.

Dush began with a hearing this month at which he emphasized that “this investigation is not about overturning the results of any election.”

On Wednesday, the Republican-controlled committee voted along party lines to subpoena the Pennsylvania Department of State for a variety of records, including communications with county elections officials, copies of election guidance and policies, and election worker training materials. The subpoena also demands information on all registered voters in the 2020 general and 2021 primary elections, including names, dates of birth, driver’s license numbers, last four digits of Social Security numbers, and addresses, as well as the same information broken out by method of voting.

In addition, it requests a complete record of “all changes to voter records made between May 31, 2020, and May 31, 2021,″ a list that can include millions or tens of millions of changes if vote history updates are included alongside changes to the voter roll such as new registrations, updates to existing voters’ addresses, changes in party affiliation, and the removal of dead or inactive voters.

Democrats immediately vowed to challenge the subpoena in court, resulting in the Friday lawsuit.

The subpoena was delivered Wednesday and gives the Department of State 16 days to meet a deadline of 4 p.m. on Oct. 1.

Staff writer Andrew Seidman contributed to this article.