The attorney representing President Trump in the battle over his tax returns says the IRS shouldn't divulge anything to House Ways and Means Committee Chairman Richard Neal until Justice Department lawyers issue a formal legal opinion on the constitutionality of the matter.

Neal, a Massachusetts Democrat, asked the IRS on Wednesday to give over six years' worth of Mr. Trump's tax returns to the committee. But in a letter to Treasury Department General Counsel Brent McIntosh on Friday, Trump attorney Will Consovoy said he doubted the constitutionality of Neal's request, and warned about the "dangerous precedent" it could set.

But perhaps the most significant lines come in the final paragraph of the four-page letter, when Consovoy asked the IRS to let the Justice Department's Office of Legal Counsel get involved.

Get Breaking News Delivered to Your Inbox

"Finally, given the unprecedented nature of Chairman Neal's request, the IRS should refrain from divulging the requested information until it receives a formal legal opinion from the Justice Department's Office of Legal Counsel," Consovoy wrote in the letter, which was obtained by CBS News.

Consovoy argues in his letter that Neal's request "flouts" the "fundamental constitutional constraints" protecting privacy and First Amendment rights. "While the committee has jurisdiction over taxes, it has no power to conduct its own examination of individual taxpayers," Consovoy wrote.

"Even if Ways and Means had a legitimate committee purpose for requesting the president's tax return and return information, that purpose is not driving Chairman Neal's request. 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," Consovoy added.

Consovoy expressed further concerns about how granting such a request could pave the way for more such requests.

"As Secretary Mnuchin recently told Congress, he is 'not aware that there has ever been a request for an elected official's tax returns.' For good reason. It would be a gross abuse of power for the majority party to use tax returns as a weapon to attack, harass, and intimidate their political opponents. Once this Pandora's box is opened, the ensuing tit-for-tat will do lasting damage to our nation."

Mr. Trump, asked about whether he will urge the Treasury Department not to comply with the request, said Neal will have to speak with both his lawyers and Attorney General William Barr.

"They'll speak to my lawyers. They'll speak to the attorney general," Mr. Trump told reporters Thursday.

Cosovoy is also representing Mr. Trump in a separate emoluments case involving allegations that Mr. Trump is personally and illegally profiting from foreign entities.