U.S. Treasury Secretary Steven Mnuchin has refused to comply with a subpoena issued by the House Ways and Means Committee that demands the release of President Trump’s tax returns.

Secretary Mnuchin responded to the subpoena on Friday, May 17, with a single-page letter to Committee Chairman Richard E. Neal (D-Mass.). In the letter, Mnuchin states that the Treasury Department had deemed the committee’s request invalid. “We are unable to provide the requested information in response to the Committee’s subpoena,” he concludes. Mnuchin felt the subpoena “lacks a legitimate legislative purpose.”

The House Ways and Means Committee first requested Trump’s tax records in April. It seeks both his business and personal tax returns for the six years between 2013 and 2018. The House Committee is asserting that it needs Trump’s returns released as it considers legislative proposals relating to how the IRS audits sitting presidents. However, Mnuchin has argued that Democrats just want to expose Trump’s returns for political purposes.

Both the committee and the U.S. Treasury Department now expect that their dispute will move to the courts for adjudication. Chairman Neal spoke to reporters Friday, indicating that House Democrats are planning to “proceed to court as quickly as [this coming] week.”

In addition to taking legal action, Congress would also have the option to hold Trump administration officials in contempt, which could result in fines or even detention for those who fail to comply with congressional subpoenas. However, Neal told reporters that he does not want to pursue a contempt vote, stating, “The better option for us is to proceed with a court case.”