President Joe Biden in recent weeks has championed COVID-19 vaccine booster shots as a means of strengthening protection against the virus, but now experts are reportedly advising the president’s administration to back off, arguing the science doesn’t justify widespread use of the third shot.

According to Politico, several prominent doctors and scientists outside of the administration held a call with federal officials last week advising against promoting COVID-19 booster shots. These experts said that current data on vaccine performance doesn’t support using booster shots widely to reduce the risk of a breakthrough COVID-19 infection.

The call reportedly took place on Sept. 27, the same day Biden made a big deal out of receiving his booster shot, and included White House chief medical adviser Dr. Anthony Fauci and policy adviser Cameron Webb, as well as the heads of the Food and Drug Administration and Centers for Disease Control and Prevention. The outside experts advised that booster shots should only be given to “people most at risk of severe Covid-19 to reduce hospitalizations and deaths,” Politico reported.

For weeks, the messaging from Biden’s White House strongly supported securing booster shots for every vaccinated American. But the FDA and the CDC have yet to authorize the use of COVID-19 booster shots. A week before the call took place, the CDC’s independent vaccine advisory committee recommended that the Pfizer-BioNTech booster shot be reserved for high-risk groups like the elderly or the immunocompromised.

The recommendation contradicted messaging from Biden and particularly from Fauci, who has repeatedly said that people will likely need a third vaccine dose to be considered fully vaccinated against COVID-19.

Politico’s sources described the call as “the tensest one to date,” highlighting Fauci’s disagreements with the outside expert’s position on boosters.

On the 2020 campaign trail, Biden promised to “follow the science” on COVID-19. But despite the recommendations from the FDA and CDC, he has publicly maintained that booster shots will soon become available “across the board.”

In the coming weeks, Biden officials will need to decide if Moderna and Johnson & Johnson vaccine recipients will need booster shots, whether people can receive doses of two different vaccines, and whether the Pfizer shot will be approved for children younger than 12.

The report on this call highlights growing disagreement between Biden and his political appointees and the scientific experts inside and out of the federal government’s health agencies.