(CNN) After months of promises and amid growing frustration from even some of his Democratic colleagues, House Ways and Means Committee Chairman Richard Neal formally requested six years of Donald Trump's tax returns on Wednesday -- a move that will likely trigger one of the biggest political and legal showdowns of the President's first term.

The request from the Massachusetts Democrat, which came in the form of a letter to IRS Commissioner Charles Rettig and was first reported by CNN's Lauren Fox, was long expected. Under a little-known (until recently) 1924 provision in the IRS code, the chairman of the Ways and Means Committee, which is charged with setting tax policy, is allowed to request anyone's tax return -- including the President of the United States -- as long as they can show that it is part of either an investigation or fulfilling Congress' oversight role.

With Neal making good on his promise in the days following Democrats retaking the House in the 2018 midterms, the ball has been firmly smacked into Trump's court.

Asked about Neal's move on Wednesday, Trump seemed disinclined to instruct the IRS and the broader Treasury Department to comply with the request.

"Now, we're under audit, despite what people said," Trump said. "We're working that out as -- I'm always under audit it seems. But I've been under audit 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 that."

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