The White House has told former staffers Hope Hicks and Annie Donaldson not to comply with subpoenas from House Judiciary Democrats to produce documents to the committee, officials said -- the latest escalation in a showdown over documents related to the Russia investigation.

Hicks, former White House communications director, and Donaldson, former chief of staff to ex-White House Counsel Don McGahn, were told by current Counsel Pat Cipollone not to produce the documents, a source familiar with the situation told Fox News. A letter was also sent to Committee Chairman Jerry Nadler, D-N.Y., informing him of the instruction.

NADLER SUBPOENAS HOPE HICKS, ANNIE DONALDSON AFTER MCGAHN DEFIES PANEL'S DEMANDS

"The subpoenas seek documents related to matters that were subjects of the investigation conducted by Special Counsel Robert S. Mueller, III. Those documents include White House records that remain legally protected from disclosure under longstanding constitutional principles, because they implicate significant Executive Branch confidentiality interests and executive privilege," the letter says.

The instructions are the latest in a standoff between the White House and congressional Democrats amid investigations into whether President Trump obstructed justice in Mueller’s Russia probe.

Nadler said on Tuesday that there was “no lawful basis” for the block and said that Hicks, who now serves as executive vice president and chief communications officer of Fox Corporation, has agreed to turn over some documents related to her work on the Trump campaign.

"Federal law makes clear that the documents we requested -- documents that left the White House months ago -- are no longer covered by executive privilege, if they ever were,” he said in a statement.

"The President has no lawful basis for preventing these witnesses from complying with our request. We will continue to seek reasonable accommodation on these and all our discovery requests and intend to press these issues when we obtain the testimony of both Ms. Hicks and Ms. Donaldson."

But a spokesperson for Ranking Republican Rep. Doug Collins, R-Ga., said the White House did not explicitly direct Hicks and Donaldson to defy a subpoena.

"In fact, the White House again invited Judiciary Committee Democrats to direct their requests there, which they have yet to do. This isn’t about ignoring subpoenas—it’s about following standard operating procedure for documents that don’t belong to Ms. Hicks or Ms. Donaldson, may be subject to certain privileges, and they, therefore, are unable to provide," the spokesperson told Fox News.

The subpoenas had ordered the documents be turned over by Tuesday, and the committee had called for Hicks and Donaldson to testify later this month.

The subpoenas specifically requested, among a slew of other materials, information from Hicks concerning the "'Republican Platform 2016' provisions relating to Russia and Ukraine, including, but not limited to, the exclusion of language related to providing lethal defensive weapons to Ukraine and the inclusion of language about providing 'appropriate assistance' to the armed forces of Ukraine."

Hicks was also requested to turn over information on "any loan, financing transaction, or capital investment by the Russian Federation, any Russian national, any Russian business, or any other Russian entity to the Trump Organization, Donald Trump, Ivanka Trump, Jared Kushner, or any of their Business Interests. This request shall include the period from January 1, 2015 to the present and shall exclude documents relating to the purchase of individual condominium, cooperative, or apartment units."

WHITE HOUSE BLOCKS MCGAHN FROM PRODUCING DOCUMENTS SUBPOENAED BY HOUSE JUDICIARY COMMITTEE

Mueller, who announced last week that the special counsel’s office was closing down, found no evidence of the Trump campaign colluding with the Russian government, and did not reach a conclusion on whether the president obstructed justice.

"If we had had confidence that the President clearly did not commit a crime, we would have said so," he said in a statement last week. "We did not, however, make a determination as to whether the President did commit a crime."

Hicks was a member of Trump’s inner circle during many of the events in the report, while Donaldson was featured repeatedly in Mueller's report, largely because of notes she took around the time that Trump fired former FBI Director James Comey.

Last month, the White House also blocked McGahn from producing documents related to the probe, similarly saying such documents “implicate significant Executive Branch confidentiality interests and executive privilege.”

Fox News' Chad Pergram and Alex Pappas contributed to this report.