Washington CNN  — 

White House chief of staff Mark Meadows told Food and Drug Administration Commissioner Dr. Stephen Hahn he needed to grant an emergency use authorization for Pfizer/BioNTech’s coronavirus vaccine by the end of Friday, and if not, he would have to resign, an administration official and a source familiar with the situation tell CNN.

Another person familiar with the matter, who also confirmed the demand that the vaccine be authorized by the end of Friday, said President Donald Trump has been venting about the FDA chief since the vaccine was rolled out in the UK earlier this week.

The FDA announced the authorization late Friday night.

Meadows and Hahn had a call Friday morning. A White House official said they do not comment on private conversations but the chief “regularly requests updates on the progress toward a vaccine.”

Hahn quickly disputed the description of the conversation, which was first reported by The Washington Post, but the news is likely to raise additional questions about the extent to which Trump administration political interests are involved with the vaccine authorization process, and could undermine public confidence in the effort.

“This is an untrue representation of the phone call with the Chief of Staff. The FDA was encouraged to continue working expeditiously on Pfizer-BioNTech’s (emergency use authorization) request,” Hahn said in a statement Friday afternoon. “FDA is committed to issuing this authorization quickly, as we noted in our statement this morning.”

On Saturday, Hahn denied that political pressure led to a quicker than normal decision to issue emergency authorization for Pfizer’s coronavirus vaccine.

“The representations in the press that I was threatened to be fired if we didn’t get it done by a certain date is inaccurate,” Hahn said during a joint news conference with Dr. Peter Marks, who heads the FDA’s vaccine and biologicals branch.

“Dr. Marks and I have been very clear from the beginning that we are going to maintain the integrity of the scientific process. We are going to let our scientists do their job and review and go through the fairness of that review – the gold standard, if you will,” he added.

“But we also recognize the urgency of the situation, and so we have said repeatedly we will work as quickly as we can to come to a decision and that’s what we did.”

A White House official familiar with the conversation between Meadows and Hahn said it’s doubtful the FDA commissioner would have actually been fired. The blunt warning from the chief of staff that he might as well resign if Pfizer’s emergency use authorization wasn’t granted by Friday was a larger sign of the President’s frustration, this person said.

Public health experts have been fearful all along that White House officials would put undue pressure on the authorization process and, in turn, compromise public confidence in the vaccine, a source close to the White House coronavirus task force told CNN.

This source said it’s unclear why Meadows would make such a threat so late in the process, at a time when the authorization was expected imminently.

Dr. Moncef Slaoui, the head of the US government’s effort to develop a vaccine against Covid-19, told CNN’s Jake Tapper on “The Lead” Friday he was concerned about the reports’ potential effect on undermining confidence in the vaccine’s safety.

“Yes, I think there is an opportunity there for people to see undue pressure if the story is right,” he said while also defending the FDA’s authorization process, which he described as “an effective, transparent, thorough, in-depth review.”

Trump has grown impatient with the authorization process in recent weeks, with one person familiar with the President’s thinking telling CNN that Trump wants to rush out as many vaccines as possible before he leaves office.

On Friday, he called the FDA “a big, old, slow turtle.”

“Get the dam vaccines out NOW, Dr. Hahn @SteveFDA,” Trump tweeted. “Stop playing games and start saving lives!!!”

President-elect Joe Biden, in remarks Friday afternoon at an event announcing additional top administration picks, did not address the news of the Meadows demand to Hahn but urged the public to have faith in the vaccine and expressed gratitude “to the scientists and the public experts who evaluated its safety and efficiency, free from political influence.”

“I want to make it clear to the public, you should have confidence in this – there is no political influence,” Biden said. “These are first-rate scientists taking their time looking at all of the elements that need to be looked at. Scientific integrity led us to this point.”

This story has been updated with additional comments from Hahn on Saturday.

CNN’s Caroline Kelly and Veronica Stracqualursi contributed to this report.