WASHINGTON — Steven Mnuchin, the Treasury secretary, signaled on Thursday that he would likely block a congressional request to obtain President Trump’s tax returns on privacy grounds, setting up a potential legal battle if Democrats follow through with plans to request those documents.
During an occasionally testy hearing before the House Ways and Means Committee, Mr. Mnuchin was peppered with questions from Democrats about whether he believes Congress has the authority to access the tax returns of American citizens in general and the president in particular.
Mr. Mnuchin told lawmakers that if a request was made he would consult the Treasury Department’s legal team and follow the law. But he indicated that taxpayer privacy, including that of the president, is paramount.
“We will protect the president as we would protect any individual taxpayer under their rights,” Mr. Mnuchin said.
Mr. Mnuchin said he is expecting House Democrats, who now control that chamber, to request the returns but insisted he has not spoken to Mr. Trump or his attorneys about how to handle a request. He did not elaborate when pressed about other possible conversations regarding the returns.
An obscure provision in the tax code, passed after the Teapot Dome scandal of the 1920s, states that the leaders of the House and Senate tax-writing committees are authorized to request taxpayer information from the Internal Revenue Service and asserts that “the secretary shall furnish such committee with any return or return information specified in such request.”
Treasury officials have indicated previously that the nature of the request would determine whether the I.R.S. is required by law to furnish a taxpayer’s returns. A request made for political purposes would be unlikely to meet the legal test, the Treasury has said.
House Democrats asserted that numerous requests for tax returns are made every year for administrative purposes and that Treasury officials never interfere in those cases.
“I’m not aware that there has ever been a request for an elected official’s tax returns,” Mr. Mnuchin said.
Representative Lloyd Doggett, the Texas Democrat who questioned Mr. Mnuchin on the tax issue, found the response to be unpersuasive.
“What he said today was little more than mumble jumble double talk,” Mr. Doggett said after the hearing.