Washington (CNN) The top Democrat on the Senate Finance Committee on Thursday threatened to hold up Treasury Department nominees unless the agency responds to requests for information about President Donald Trump's personal tax returns.

"If the Treasury Department refuses to answer our questions, I am prepared to again place a hold on department nominees as I did previously when routine requests for information went unanswered," Sen. Ron Wyden of Oregon wrote. "Congress needs to take action to force the administration to comply with oversight."

Trump has broken with decades of presidential precedent by refusing to make his personal tax information public, and has retained his interest in the Trump Organization while in office.

Treasury Secretary Steven Mnuchin has refused to comply with a subpoena from House Democrats for six years of Trump's tax returns, citing Department of Justice legal advice. Ways and Means Chairman Richard Neal has requested the documents under an obscure statute that grants the heads of tax-writing committees access to tax returns for oversight purposes.

Trump has several nominees to the Treasury Department currently waiting for Senate confirmation, including agency general counsel Brent McIntosh, who has been nominated to be Treasury undersecretary for international affairs. Other nominees include Brian McGuire, nominee for assistant secretary for legislative affairs; Michael Faulkender, the nominee for assistant secretary of economic policy; Brian Callanan, the nominee for general counsel and Geoffrey William Seiji Okamoto, nominated for deputy undersecretary.

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