(Bloomberg) -- Treasury Secretary Steven Mnuchin said a request from House Democrats for President Donald Trump’s tax returns is under review and that "we will follow the law."

“We did receive the request" for six years of Trump’s personal tax returns as well as those for several of the president’s business entities, Mnuchin told a House Appropriations subcommittee on Tuesday.

Several members of the Trump administration, including White House chief of staff Mick Mulvaney, have called the request a political attack and a violation of Trump’s privacy and have vowed to fight it.

Mnuchin, however, said it would be “premature at this point to make any specific comments. It is being reviewed by the legal department and we look forward to responding to the letter."

The Treasury secretary said he has not spoken to Trump or Mulvaney about the request, but said he didn’t know if other Treasury officials had.

House Ways and Means Chairman Richard Neal last week asked Internal Revenue Service Commissioner Charles Rettig to hand over the president’s filings. He said the committee needed the returns as part of their oversight duties to make sure the IRS is properly auditing the president. But Democrats have long wanted Trump’s tax returns to see what foreign financial dealings he may have, whether he always followed the law, and if he benefited from the 2017 Republican tax overhaul.

The request is likely to become a protracted legal battle. William Consovoy, one of Trump’s lawyers, has advised the IRS and Treasury Department to refuse the request until a legal opinion can be issued. If the department refused to hand them over, Democrats would likely sue. And if the request ends up in the courts, the issue could linger unresolved until after the 2020 presidential election.

Trump has said his returns are under audit and that he doesn’t intend to turn anything over until that is finished. No law prevents a taxpayer from releasing returns that are under audit.

Federal law allows the Ways and Means and Senate Finance committees and the Joint Committee on Taxation to ask the IRS for the returns of any filer, but some legal scholars say a request requires Congress to have a legislative purpose, including general oversight. The committees could then vote to make those documents public.

Mnuchin told the Ways and Means Committee in March that he’d follow the law if the committee requested the returns. But he added, “We will protect the president as we would protect any individual taxpayer under their rights.”

Senior Republicans, including Senate Finance Committee Chairman Chuck Grassley and Kevin Brady, the ranking GOP member on House Ways and Means, have said Democrats are using the tax code to go after a political foe.

Congress released private tax information during the Watergate scandal involving President Richard Nixon and during the more recent allegations that the IRS targeted Tea Party groups during President Barack Obama’s administration.

Trump broke with 40 years of presidential campaign tradition in refusing to release his personal tax returns before he was elected, claiming at one point that he was under audit, and at another that it was an invasion of his privacy. After the election, White House officials said he wouldn’t release them because Americans had elected him without seeing the returns.

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