House Democrats on Saturday increased their demands for the IRS to give them access to President Trump’s tax returns -- foreshadowing a lengthy legal battle in the courts

House Ways and Means Committee Chairman Richard Neal, D-Mass., told the IRS that the law gives Congress a right to the six years of Trump’s personal and business tax returns, and set a deadline for the agency to respond by April 23.

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Neal told IRS Commissioner Charles Rettig that if he does not respond to his letter, Neal will interpret that as denying the request, setting the stage for a potential court battle.

The Treasury Department missed an April 10 deadline last week set by Democrats to deliver the tax returns, and Secretary Steven Mnuchin said the department hadn’t decided whether to comply with the request.

“It is not the proper function of the IRS, Treasury, or Justice to question or second guess the motivations of the Committee or its reasonable determinations regarding its need for the requested tax returns or return information,” Neal wrote.

The letter marks the latest in a yearslong effort by Democrats to get access to Trump’s financial documents. Neal asked for Trump’s personal and business returns from 2013-18. Democrats say it is within their mandate of congressional oversight, but the unprecedented move has been opposed by Republicans.

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Trump has said repeatedly throughout the 2016 presidential campaign and his presidency that he can’t make public his tax returns because he is under audit.

A lawyer for Trump said in a letter last week that the efforts are an attempt to harass a political opponent and that it would set a “dangerous precedent” for the agency to turn them over.

“For good reason, it would be a gross abuse of power for the majority 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,” William S. Consovoy said in a letter to the Treasury’s general counsel.

In his letter, Consovoy said that Neal “cannot legally request” the information as the tax code guards taxpayer privacy with the exception of certain conditions -- which he says are not met.

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“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,” he 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,” he added.

The Associated Press contributed to this report.