The Biden administration is currently developing a plan that would require most international travelers entering the U.S. from all countries to be fully vaccinated against COVID-19, a White House official said Wednesday.

The U.S. is keeping international travel restrictions in place for the time being due to the spread of the delta variant and rising domestic cases of the coronavirus. The new plan would be operationalized when the U.S. begins to lift restrictions on international travel.

The White House official said that interagency working groups are currently working to develop a plan for “a consistent and safe international travel policy” that would involve a phased approach that would require foreign nationals traveling to the U.S. to be fully vaccinated “with limited exceptions.”

“Currently, the interagency working groups are developing a policy and planning process to be prepared for when the time is right to transition to this new system,” the official said.

Reuters first reported that Biden administration officials are developing the plan for international travelers.

It’s unclear precisely when the U.S. will lift restrictions on travel from Mexico, Canada, Europe and other countries. The White House said in late July that it would keep restrictions in place, citing the delta variant.

After steeply declining from the start of the year, coronavirus cases have been on the rise again as vaccination rates have slowed. The Biden administration is working to convince millions of eligible Americans who have not yet gotten vaccinated to do so as quickly as possible. Currently, about 70 percent of U.S. adults have received at least one dose of the coronavirus vaccine.

States like Florida, Texas and Arkansas are seeing large numbers of coronavirus infections.

While the U.S. has kept restrictions in place, other countries have moved to open their borders to vaccinated travelers. The European Union is allowed entry of vaccinated U.S. travelers, and so has the United Kingdom and Canada.