FILE PHOTO: U.S. President Donald Trump responds to reporters questions as he heads to the Marine One helicopter to fly to visit injured members of the U.S. military at Walter Reed National Military Medical Center in Maryland from the White House in Washington, October 4, 2019. REUTERS/Kevin Lamarque

WASHINGTON (Reuters) - The U.S. Treasury Department’s internal watchdog is investigating how the agency handled a congressional request for President Donald Trump’s tax returns, it said on Friday.

The Democratic chairman of the House of Representatives Ways and Means Committee, Richard Neal, requested the investigation, said Richard Delmar, Treasury’s acting inspector general.

Neal asked the office of the inspector general to “inquire into the process by which the department received, evaluated, and responded to the committee’s request for federal tax information,” Delmar said. The watchdog was “undertaking that inquiry,” he added.

The Republican president has refused to make his tax returns public, unlike his predecessors. The House Ways and Means committee launched a probe into Trump’s taxes earlier this year.

The internal probe was first reported by the New York Times, which earlier reported that Trump and his family business had underpaid federal taxes for years.

Treasury Secretary Steven Mnuchin, a member of Trump’s cabinet, refused Neal’s April request for six years of Trump’s individual and business federal tax returns. Neal subpoenaed the returns, and Mnuchin rejected the subpoena.