The White House has denied taking any action to prevent that testimony.
"I hope she testifies. I look forward to it," White House press secretary Sean Spicer said today. "We had no objection to her going forward ... To suggest in any way, shape or form that we stood in the way of that is 100 percent false."
Pence repeated the false information when asked about the situation in January, prompting Yates to inform the White House that Flynn may have misled Pence and other senior officials about his communications with Kislyak.
In her testimony slated for today, Yates was expected to offer a firsthand account of her discussions with the White House in January.
"Such communications are likely covered by the presidential communications privilege and possibly the deliberative process privilege. The president owns those privileges. Therefore, to the extent Ms. Yates needs consent to disclose the details of those communications to HPSCI [House Permanent Select Committee on Intelligence], she needs to consult with the White House. She need not obtain separate consent from the Department," a Justice Department official wrote to O'Neil on Friday.
O'Neil then wrote his letter to the White House, insisting any claim of executive privilege had been waived "as a result of the multiple public comments of current senior White House officials describing the January 2017 communications. Nevertheless, I am advising the White House of Ms. Yates' intention to provide information."
The White House never responded to his letter — which he wrote would be taken as a green light for Yates to move forward.
"We didn't respond. We encouraged them to go ahead," Spicer said, adding that the White House never considered invoking executive privilege to block her testimony.
Spicer also insisted that Nunes' decision to call off today's hearing had nothing to do with any pressure from the White House. Nunes himself said that no one directed him to postpone the hearing.
Jack Langer, a spokesman for Nunes, similarly denied any coordination between the committee and White House over Yates' testimony.
"Neither Chairman Nunes nor any Intelligence Committee staff members had any communication with the White House whatsoever about Sally Yates' testifying to the committee," Langer said in a statement. "The only person the committee has spoken to about her appearing before the committee has been her lawyer. The committee asked her to testify on our own accord, and we still intend to have her speak to us."
The Washington Post first reported on the letters between O'Neil and the Trump administration.
Yates, an Obama administration appointee, was fired by Trump on Jan. 30 after she instructed the Justice Department not to defend his controversial executive order limiting travel and immigration from seven countries in Africa and the Middle East.
Nunes and the congressional inquiry he's leading into alleged Russian interference have come under increasing criticism in recent days, after he first claimed he had discovered "concerning" evidence that the Trump campaign was monitored after the election.
Last week, Nunes announced he obtained "dozens of reports" showing the U.S. intelligence community — through its "normal foreign surveillance" — "incidentally collected information about U.S. citizens involved in the Trump transition."
But Nunes cannot say whether Trump or any of the president's associates personally participated in the communications that were intercepted, meaning it's possible that the information he's citing merely refers to foreign officials talking about Trump transition team members.
Nunes has yet to share the information with other members of the House Intelligence Committee or further explain what it shows. He said Tuesday that he will "never" reveal sources or methods to fellow committee members but that he still hopes to share the documents.
On Monday, without identifying his source, Nunes acknowledged he obtained the information while on White House grounds, an admission Democrats said should force him to at least recuse himself from the committee probe tied to Russia.
ABC News' Mary Bruce, Jonathan Karl, Pierre Thomas and Adam Kelsey contributed to this report.