As White House officials rushed to shape last week’s sweeping new vaccine mandates, they debated the idea of requiring international air travelers to be vaccinated before boarding a plane, as part of a larger effort to persuade more Americans to get immunized, according to two people familiar with the plans.

Some aides argued that other countries already require vaccinations to fly and that the United States should join their ranks, according to an administration official. But others said mandates work best when they require people to prove they are immunized only once – like at work – rather than repeatedly, like every time they board a plane.

The idea was shelved, but top White House officials say that proposal and similar ones are still under consideration – including, potentially, a broader vaccine mandate that would include domestic air travel.

“We’re discussing it,” Anthony Fauci, President Joe Biden’s chief medical adviser, said about the idea of a broader requirement in an interview. “It’s on the table for discussion.”

White House officials stressed that no additional mandates are imminent, as the Biden administration is still sorting through how to implement the ones announced last week.

The debate over an airplane mandate, which many public health officials say is a logical next step, highlights Biden’s struggle to balance public health needs with practical, economic and political considerations. Some at the White House warn, for example, that an air mandate could prompt frustratingly long lines at airports.

Either way, Biden’s top advisers say that significantly more measures may be needed to convince – or coerce – Americans to get vaccinations, as more than 70 million Americans who qualify for coronavirus shots have not gotten them.

That could mean more social tumult ahead, since Republicans are increasingly embracing a no-mandate message. GOP governors have announced lawsuits to block last week’s actions, and House Minority Leader Kevin McCarthy, R-Calif., on Monday tweeted, “NO VACCINE MANDATES.”

Requiring vaccines for air travel would be a big step beyond Biden’s announcement last week that businesses with more than 100 employees must require their workers to get vaccines or regular tests. Biden also ordered all federal employees to get shots and said most health care facilities that get Medicare or Medicaid funding will now have to immunize their workers.

In a departure for the disciplined Biden White House, some of the disagreements about an air travel mandate have broken into the open. Fauci, for example, applauded the idea in an interview for The Skimm podcast, saying, “I would support that if you want to get on a plane and travel with other people, that you should be vaccinated.”