Congress and the Trump administration are inching closer to a legal fight over President Trump’s tax returns.

House Ways and Means Chairman Richard Neal, D-Mass., wrote Treasury Secretary Steven Mnuchin on Saturday with a new deadline to transmit Trump’s tax returns after Mnuchin missed Neal's original April 10 deadline. The Ways and Means chairman now wants the administration to provide Trump’s tax returns to his committee by April 23.

“I am aware that concerns have been raised regarding my request and the authority of the Committee. Those concerns lack merit,” wrote Neal. “Moreover, judicial precedent commands that none of the concerns raised can legitimately be used to deny the Committee’s request.”

Neal added that the law allowing him to request and review those returns is “unambiguous,” and that he would view Mnuchin as violating the law if he blocked cooperation by the new deadline he set on Saturday.

“Please know that, if you fail to comply, your failure will be interpreted as a denial of my request,” said Neal.

Neal had requested six years' worth of Trump’s personal tax returns, as well as a portion of his business returns, directly from IRS Commissioner Charles Rettig. But Mnuchin instead responded by saying the IRS, which acts as an independent agency but is a part of Treasury, would not meet the April 10 deadline set by Neal.

Mnuchin also echoed a request made to the IRS by Trump’s personal attorneys, asking that the tax collection agency consult with the Department of Justice before cooperating with Neal’s request.

This is the first time Congress has requested sensitive tax information from the president, brought on by the fact that Trump was the first presidential candidate in decades not to release his tax returns.

Congressional Republicans argue that the request sets a dangerous precedent for that power, while Democrats maintain it’s a necessary oversight of federal tax law, including the extent that the IRS audits and enforces federal tax laws with regards to the president.

Under a section law put in place following a major bribery scandal in the 1920s, the chairman of the Ways and Means Committee can request and obtain tax returns of individuals or businesses. But that information typically must be treated as confidential by anyone who reviews it, and unauthorized disclosure can be punished by up to five years in prison. That law says the returns “shall” be provided upon request from the chairman of that committee, the Senate Finance Committee, or the chief of staff of the nonpartisan Joint Committee on Taxation that routinely reviews tax return information.