A U.S. House of Representatives panel filed suit on Tuesday against the U.S. Treasury and the Internal Revenue Service, according to a federal lawsuit, as it wrangled to obtain U.S. President Donald Trump’s tax returns.

The Democratic-led House ways and means committee filed the lawsuit in U.S. District Court for the District of Columbia after the Treasury Department refused a request for tax information about the Republican president.

“In refusing to comply with the statute, Defendants have mounted an extraordinary attack on the authority of Congress to obtain information needed to conduct oversight of Treasury, the IRS, and the tax laws on behalf of the American people,” the lawsuit said.

Ways and means chairman Richard Neal said in May he was consulting with lawyers on how best to enforce his subpoena to get Trump’s tax returns.

Congressional committees investigating Trump and his administration have been working to enforce subpoenas after White House efforts to stymie investigations on a range of issues by House panels.