A standoff between the Trump administration and congressional Democrats over President Donald Trump’s tax returns is headed for a potential lengthy court battle, after administration officials have repeatedly flouted a federal law that grants Congress access to tax information.

Treasury Secretary Steven Mnuchin on Friday refused to comply with a congressional subpoena seeking six years of the president’s tax returns — marking the fourth time that the Treasury Department has refused Democratic lawmakers’ request for this information.

Mnuchin announced his decision in a letter to House Ways and Means Committee Chairman Richard Neal (D-MA) just a few minutes before the 5:00 p.m. ET deadline to deliver the tax documents. In the letter, Mnuchin wrote that the Treasury Department is not “authorized” to release Trump’s tax returns because Congress’ request for the documents “lacks a legitimate legislative purpose.”

Neal responded by emphasizing that, due to the 1924 law that stipulates the IRS is supposed to turn over tax documents to the congressional committees responsible for crafting tax laws, the department cannot make this determination.

“The law, by its terms, does not allow for discretion as to whether to comply with a request for tax returns and return information,” he wrote.

Neal initiated the inquiry for Trump’s tax returns more than a month ago.

Neal first asked Mnuchin to hand over the tax documents by April 10. When Mnuchin missed that deadline, Neal set a new deadline for April 23. Mnuchin missed that deadline as well, saying that he was waiting for guidance from the Justice Department and that he would make a decision by May 6. Then, on May 6, Mnuchin announced that he had decided not to fulfill the request. Neal responded on May 10 with a subpoena.

It’s unclear what will happen next. Neal has previously indicated that he plans to take the matter to court. Speaking with reporters on Friday as the 5:00 p.m. ET deadline neared, Neal said that if the administration refused to comply with the subpoena, “the result will be that we will likely proceed to court as quickly as next week.”

After the deadline passed, Neal released a new statement saying he is “consulting with counsel on how best to enforce the subpoenas moving forward.”

A court case could stretch on for months or even years — setting up a situation where the matter may not be resolved before Trump leaves office.

Some Democratic lawmakers on the Ways and Means Committee have pushed to exercise their congressional power to force compliance through other means, like imposing fines or jail time for the officials who are ignoring their subpoenas.

We will see them in federal court and will pursue any avenue we can to bring this lawless administration to respect our Constitution. This is now a constitutional crisis.

— Bill Pascrell, Jr. () May 17, 2019

Rep. Bill Pascrell Jr. (D-NJ), told The New York Times on Friday that the committee should not rely only on the court system to resolve the matter, which he believes will “absent the Congress from their own responsibilities.”

“I think that’s a very dangerous position for us to be in,” he said.