WASHINGTON – Democrats officially sent a letter to the IRS demanding President Donald Trump's personal tax returns and the returns for his businesses and revocable trust, launching what is likely to lead to a legal battle between Congress and the executive branch.

House Ways and Means Committee Chairman Richard Neal, D-Mass., sent a letter Wednesday to IRS Commissioner Charles Rettig demanding copies of Trump's taxes from 2013 through 2018. He gave Rettig until next Wednesday to comply with the request.

The request probably will launch a prolonged court battle. It is the first such demand for a sitting president’s tax information in 45 years.

Democrats have been trying to get their hands on Trump's tax returns since he flouted tradition and refused to release them during the 2016 presidential campaign. When he took office, Trump continued to keep the documents private, arguing that they were under audit. Vice President Mike Pence has released his returns.

The president said he was "not inclined" to allow Democrats access to his tax returns.

"We are under audit, despite what people said, and working that out. I'm always under audit, it seems, but I've been under audit for many years because the numbers are big, and I guess when you have a name, you're audited. But until such time as I'm not under audit, I would not be inclined to do it," Trump said.

The top Republican on the House Ways and Means Committee blasted the request, saying Democrats were "weaponizing our nation’s tax code by targeting political foes."

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After the request, Rep. Kevin Brady, R-Texas, wrote a letter to Treasury Security Steven Mnuchin arguing that the request violates the law and asking Mnuchin, who oversees the IRS at the Treasury Department, to deny it.

"The use of the committee's authority to access and make public the tax returns of a single individual for purely political purposes would not only set a dangerous precedent, but it also undermines the core intent of the law," Brady wrote.

Neal argued in his letter to the IRS that his request stemmed from a policy interest. He said his role in heading the committee comes with "a responsibility to ensure that the Internal Revenue Service is enforcing the laws in a fair and impartial manner."

Neal said his request was made to investigate whether the IRS had indeed examined Trump's taxes, which he noted is required under the agency's policy.

"This practice is IRS policy and not codified in the Federal tax laws," he wrote. "It is necessary for the Committee to determine the scope of any such examination and whether it includes a review of underlying business activities required to be reported on the individual income tax return."

Along with Trump's personal taxes, Neal demanded copies of tax returns for Trump's trust and for his golf club in Bedminster, New Jersey.

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Last month, Mnuchin suggested he would protect Trump’s privacy if he received a request from House Democrats for Trump’s tax returns.

“We will examine the request, and we will follow the law … and we will protect the president as we would protect any taxpayer” regarding their right to privacy, Mnuchin said.

Neal is one of only three congressional officials authorized under a rarely used 1924 law to make a written request to the treasury secretary for anyone’s tax returns. The law says the treasury secretary “shall furnish” the requested material to members of the committee for them to examine behind closed doors. Mnuchin did not specifically say he would turn them over.

Last week, House Oversight Committee Chairman Elijah Cummings, D-Md., also demanded access to Trump's finances and asked a tax firm for documents going back 10 years. He asked tax firm Mazars USA for copies of Trump's financial documents from 2009 to 2019 – but stopped short of copies of the president's tax returns.

Cummings asked Mazars' CEO Victor Wahba for all financial documents relating to Trump's wealth that were in the firm's possession, any audits done, all communications with Trump and those representing him, along with internal communication related to any concerns over Trump's finances.

The company was noted in documents former Trump personal attorney Michael Cohen gave to the committee before his appearance in February, when he said the president encouraged him to lie to Congress and the public for Trump's protection. Cohen cast Trump as a "racist," a "con man" and a "cheat."

Contributing: Eliza Collins, USA TODAY; The Associated Press