WASHINGTON — A private lawyer for President Trump told the Treasury Department on Friday that House Democrats demanding the president’s tax returns were abusing their powers to damage him politically, and he urged the department to keep the returns secret.
The letter from William Consovoy, a lawyer whose firm also represents Mr. Trump in lawsuits related to foreign spending at his hotels, was most likely the first step in what will be a protracted effort to prevent the president’s tax information from being turned over to the House Ways and Means Committee.
“The requests for his private tax information are not consistent with governing law, do not advance any proper legislative purpose, and threaten to interfere with the ordinary conduct of audits,” Mr. Consovoy said in a statement accompanying his letter. “We are confident that this misguided attempt to politicize the administration of the tax laws will not succeed.”
It is ultimately up to the Internal Revenue Service and its parent agency, the Treasury Department, to decide whether to comply with the request.
The chairman of the House Ways and Means Committee, Representative Richard E. Neal of Massachusetts, on Wednesday formally requested that the I.R.S. hand over six years of Mr. Trump’s personal and business tax returns as part of what he said was a committee oversight investigation of tax law enforcement. He also asked for any information related to audits of Mr. Trump or several Trump business entities.
Mr. Neal, a Democrat, made the request through a little-known but frequently used provision of the federal tax code that allows Congress’s tax-writing committees to view tax information on any filer. The authority is regularly used by the committee to confidentially measure the effects of policy proposals, but there is little precedent for using it to examine the returns of a president.
Daniel Rubin, a spokesman for Mr. Neal, declined to comment on Friday’s letter.
Mr. Consovoy argued that the committee had no legitimate reason to see Mr. Trump’s returns. Mr. Consovoy was defending Mr. Trump’s privacy rights as a private taxpayer, but his arguments closely mirrored those used by Republicans in Congress who have argued against making the request.
“Even if Ways and Means had a legitimate committee purpose for requesting the president’s tax returns and return information, that purpose is not driving Chairman Neal’s request,” the lawyer wrote. “His request is a transparent effort by one political party to harass an official from the other party because they dislike his politics and speech.”
That stand hinted at a significant legal fight to come. The authority invoked by Mr. Neal, Section 6103 of the tax code, says only that the agency “shall furnish” the information upon request. Mr. Neal gave the I.R.S. until next week to comply.
If it does not, the House could go to court to try to enforce the request — a process that could take months to sort out, or longer. Democrats believe the Trump administration could present an argument similar to the one made by Mr. Consovoy on Friday, namely that Mr. Neal’s request lacks a legitimate legislative purpose and, based on past court precedent, is essentially invalid.
In making his request, Mr. Neal did not cite issues like possible tax fraud but instead said he wanted to examine audit procedures for a president.
“If Chairman Neal genuinely wants to review how the I.R.S. audits presidents, why is he seeking tax returns and return information covering the four years before President Trump took office?” the lawyer asked. “Why is he not requesting information about the audits of previous presidents?”
Mr. Consovoy said that at the very least, the I.R.S. and the Treasury Department should consult the Justice Department’s Office of Legal Counsel before handing over the information.