(CNN) The White House has instructed former White House Counsel Don McGahn not to comply with a subpoena for documents from House Judiciary Chairman Jerry Nadler, teeing up the latest in a series of escalating oversight showdowns between the Trump administration and congressional Democrats.

McGahn's decision not to comply with the subpoena could push Nadler to hold McGahn in contempt of Congress, just as he's moving to do with Attorney General William Barr after the Justice Department defied a subpoena for the unredacted Mueller report and underlying evidence.

Nadler issued a subpoena to McGahn for documents and testimony related to the committee's obstruction of justice investigation, setting a Tuesday deadline for McGahn to turn over the documents and proposing a May 21 hearing date.

In a letter sent Tuesday night, Nadler threatened McGahn with being held in contempt if he failed to appear.

"I fully expect that the Committee will hold Mr. McGahn in contempt if he fails to appear before the Committee, unless the White House secures a court order directing otherwise," Nadler wrote to McGahn's attorney, with a copy to McGahn.

He added, "A letter from the White House in service of the President's apparent goal of blocking or delaying testimony that the President believes would be politically damaging is not a basis for Mr. McGahn to violate his legal obligation to appear before the Committee."

While the White House said it would not allow McGahn to turn over documents, the White House has not relayed its position on whether it would seek to block McGahn's testimony, too, according to a person familiar with the matter.

But the committee appears poised to move forward on holding Barr in contempt, following negotiations Tuesday between Department of Justice officials and staff of the Judiciary Committee, after department officials offered to come to Capitol Hill to try to negotiate an amicable outcome to the committee's demands to see an unredacted version of the Mueller report, which the Justice Department has thus far refused to release.

Judiciary Committee Democrats leaving a separate meeting with Nadler on Tuesday afternoon said that as of now they are planning to hold a contempt vote Wednesday morning for Barr.

"Right now, all systems go for the contempt hearing," said Rep. Jamie Raskin, a Maryland Democrat. But talks will continue Tuesday night between Democrats and the Justice Department about whether a deal can be reached.

McGahn's attorney William Burck told Nadler in a letter Tuesday that McGahn was deferring to the White House's position that it maintains control of the documents Nadler had set a Tuesday deadline for McGahn to turn over.

"Here, the Committee seeks to compel Mr. McGahn to produce White House documents the Executive Branch has directed that he not produce," Burck wrote. "Where co-equal branches of government are making contradictory demands on Mr. McGahn concerning the same set of documents, the appropriate response for Mr. McGahn is to maintain the status quo unless and until the Committee and the Executive Branch can reach an accommodation."

White House Counsel Pat Cipollone wrote to Nadler Tuesday directing the committee to request the documents from the White House, and not McGahn.

"Because Mr. McGahn does not have the legal right to disclose these documents to third parties, I would ask the Committee to direct any request for such records to the White House, the appropriate legal custodian," Cipollone wrote. "The Acting Chief of Staff to the President, Mick Mulvaney, has directed Mr. McGahn not to produce these White House records in response to the Committee's April 22 subpoena."

Cipollone added that the documents in question were still protected by executive privilege "because they implicate significant Executive Branch confidentiality interests."

The White House has not yet invoked executive privilege over the material, however.

The Judiciary Committee voted last month to authorize subpoenas for McGahn and five other former White House officials who were interviewed by the special counsel's team. The committee is interested in obtaining documents from those officials regarding their preparations for their interviews with the special counsel, as part of the panel's separate investigation into possible obstruction of justice.

So far, Nadler has only issued a subpoena to McGahn, and not the other four White House officials.

Rep. Doug Collins, the top Republican on the Judiciary Committee, urged Democrats to negotiate with the White House to reach an agreement.

"As I said more than a month ago, when Democrats subpoenaed Don McGahn, they subpoenaed the wrong person," the Georgia Republican said in a statement. "The White House is nevertheless seeking to accommodate Democrats' unwieldy demands. I hope Chairman Nadler accepts this reasonable offer rather than continuing to reject good faith offers to negotiate."

McGahn was a key witness in the special counsel's report on obstruction of justice, which included an episode where Trump told McGahn to fire the special counsel, and McGahn would not do so

If the committee goes to court to try to compel McGahn to turn over records, it could lead to a test of executive privilege in the courts that could have implications for the numerous House investigations into the Trump administration.

House Democrats have argued that McGahn and other former White House officials have waived executive privilege by speaking to Mueller's team. Nadler also says that the documents he's seeking are not covered by executive privilege because they were turned over to attorneys outside the White House.

But the White House counsel's office has countered that it still has the right to invoke executive privilege with respect to congressional investigations, arguing that waiving executive privilege for Mueller's criminal investigation is not the same thing as doing so for a separate branch of government.

This story has been updated with additional developments Tuesday.