“For the same reasons, we are unable to provide the requested information in response to the committee’s subpoena,” Mr. Mnuchin said.

Mr. Mnuchin was widely expected to ignore the subpoena, as Mr. Trump has vowed to fight all subpoenas from House Democrats. The Treasury secretary has warned that allowing House Democrats to retrieve the president’s tax returns would open the door to lawmakers from both parties politicizing the Internal Revenue Service in the future.

At a Senate hearing this week, Mr. Mnuchin said that House Democrats were trying to “weaponize” the I.R.S. He said that he had not yet decided how he would respond to the subpoena, but that “you can guess which way we are leaning.” He said that the judiciary, as the third branch of government, would most likely need to settle the dispute between Congress and the executive branch, signaling the potential for a protracted court fight.

House Democrats have been weighing how to respond to the Trump administration’s defiance of congressional subpoenas. On Friday, Mr. Neal made clear his preference for avoiding retaliatory threats, to the disappointment of several of his more liberal colleagues.

Mr. Neal told reporters that he saw little value in trying to hold Mr. Mnuchin or Charles P. Rettig, the I.R.S. commissioner, in contempt of Congress. Instead, he said, he would go straight to the courts to try to enforce his subpoena, potentially as soon as next week. The case could take months or years to resolve.