President Donald Trump sued the Manhattan district attorney’s office on Thursday in an effort to squash a subpoena for eight years worth of the president’s personal and business tax returns.

The documents are being sought by state prosecutors as part of a criminal investigation into falsified business records by the Trump organization, a person familiar with the matter told The Daily Beast.

The suit, which filed in Manhattan federal court Thursday, names District Attorney Cy Vance and Mazars USA, the accounting firm that has long handled tax returns for the president and the Trump organization, as defendants.

In a statement, the president’s lawyer Jay Sekulow said he and Trump’s legal team filed a lawsuit in federal court, “ in order to address the significant constitutional issues at stake in this case.”

“In response to the subpoenas issued by the New York County District Attorney, we have filed a lawsuit this morning in Federal Court on behalf of the President in order to address the significant constitutional issues at stake in this case,” Sekulow said.

A copy of the complaint was not immediately available, and it was not clear what constitutional issues are at stake.

The subpoena was obtained late last month as part of a grand jury proceeding that was opened by Manhattan District Cy Vance, a person familiar with the matter told The Daily Beast. News of the subpoenas was first reported Monday by The New York Times.

Danny Frost, a spokesman for Vance has declined to confirm the existence of a grand jury probe or comment about it. Frost said the district attorney’s office has “received the plaintiff’s complaint and will respond as appropriate in court,” adding that prosecutors will not make any additional comments on the case as it makes its way through court.

The person familiar told the Beast that the legal precedent is high for obtaining a subpoena as part of a grand jury proceeding and the bar is similarly high to get a judge to throw it out.

The lawsuit is the strongest sign yet that the president’s legal team is extending the hardline tactics they’ve used on congressional Democrats to prosecutors.

Trump has vowed to fight “all the subpoenas” from Congress, including a subpoena from the Ways and Means Committee for access to Trump’s tax returns, which that panel is uniquely situated to obtain. The courts are currently weighing whether trump can block that subpoena—which centers on Congress’ possession of a legitimate legislative purpose for the information—and it may go to the Supreme Court. Courts are also considering a subpoena from the House Oversight Committee for financial records of Trump’s businesses, which a judge recently expedited.

The president’s team may stymie Democrats, but the application of that strategy to block prosecutors—who have far more tools and leverage at their disposal than lawmakers do—will be severely tested.

Manhattan prosecutors are seeking Trump’s personal tax documents and those of the Trump Organization from accounting firm Mazars USA, including federal and state returns dating back to 2011.

The subpoena was issued after prosecutors opened a grand jury investigation into the role Trump and the company played in the hush-money payment to adult film star Stormy Daniels, who says she had an affair with Trump, the person said. Trump has denied the affair.

Michael Cohen, the president’s former personal attorney, made the $130,000 payment to Daniels, and was subsequently reimbursed by the president and the Trump Organization.