President Donald Trump is suing House Democrats to stop them from subpoenaing his financial records.

His attorneys filed the lawsuit in federal court on Monday, targeting House Oversight Chair Elijah Cummings as the defendant. Cummings recently subpoenaed the longtime accounting firm for the Trump family and businesses, Mazars USA, for Trump’s personal and professional financial records over a 10-year period.

Cummings cited the testimony of Trump’s former personal attorney, Michael Cohen, who testified before Congress that Trump had inflated his net worth as a private citizen. In issuing the subpoena, Cummings said that Cohen’s testimony and other corroborating documents “raise grave questions about whether the [p]resident has been accurate in his financial reporting,” according to CNN.

Now Trump has filed a lawsuit to block Cummings, claiming the Democrat’s subpoena is a gross overstep of Congress’s authority under the Constitution.

The president’s legal argument is that Congress does not have an unlimited right to investigate the executive branch. Instead, its investigations must serve some kind of legislative purpose. According to the brief filed by his attorneys, Democrats do not have any plans to legislate based on the information they retrieve from Mazars, but rather they want to embarrass Trump with whatever they uncover.

“Investigations are legitimate only insofar as they further some legitimate legislative purpose. No investigation can be an end in itself,” Trump’s attorneys argue. “Chairman Cummings’ subpoena of Mazars lacks a legitimate legislative purpose. ... Its goal is to expose [p]laintiffs’ private financial information for the sake of exposure with the hope that it will turn up something that Democrats can use as a political tool against the [p]resident now and in the 2020 election.’

The lawsuit asks the district court to rule that the Cummings subpoena is invalid and unenforceable.

The subpoena and retaliatory litigation are the latest escalation in the House Democrats’ investigations of the Trump administration and in the longstanding fight to force the president to release more detailed financial information. In a major break with previous political norms, Trump refused to release his tax returns as a candidate and continued to maintain they shouldn’t be released, citing an ongoing audit.

House Democrats are intent on using their oversight authority to get a peek into the president’s books. In addition to the Cummings subpoena, House Ways and Means chair Richard Neal (D-MA) has asked the IRS to turn over Trump’s tax returns from 2013 to 2018. Neal has set an April 23 deadline; if the Trump administration refuses to cooperate, more litigation could follow.