The idea of a vaccine mandate for domestic air travel in the United States got at least partial backing from the nation’s top disease expert Monday. In a television interview, Dr. Anthony Fauci said it “is just another one of the requirements that I think is reasonable to consider.”

“When you make vaccination a requirement, that’s another incentive to get more people vaccinated,” Fauci said in the interview. “If you want to do that with domestic flights, I think that’s something that seriously should be considered.”

Currently, the U.S. only requires most foreign nationals traveling to the U.S. be fully vaccinated. Citizens and permanent residents flying in from other countries or Hawaii only need to show proof of a negative test taken within a day of boarding.

Although Fauci is a top adviser to President Joe Biden regarding COVID-19, the Biden administration has not yet endorsed the idea of a domestic air travel vaccine mandate. Two officials who spoke to the Associated Press on the condition of anonymity said President Biden’s science advisers have yet to make a formal recommendation, citing the host of logistical and legal concerns such a mandate could trigger.

Just hours before the Fauci interview, Biden said the topic of a domestic air travel vaccine mandate was discussed on a call with the National Governors Association (NGA) Monday. The video above shows clips from the call, as well as Biden’s comments afterwards.

“They asked Dr. Fauci some more questions about everything from whether or not he thought he was going to move to test at home — I mean, on air flights and that kind of thing,” Biden said after the call.

According to the White House, the call focused on a wide range of COVID-related topics, including:

• The latest science on the Omicron variant
• The use and distribution of COVID-19 treatments
• Federal partnerships and resources on testing
• Keeping U.S. schools open

While Biden told the governors that “we’re going to have your back any way we can,” NGA Chair Gov. Asa Hutchinson (R-AR) urged Biden to focus on state-based solutions.

“As you look towards federal solutions that will help alleviate the challenge, make sure that we do not let federal solutions stand in the way of state solutions,” Gov. Hutchinson said on the call. “That dries up the supply chain for the solutions that we might offer as governor.”