The U.S. military will start requiring service members to receive a COVID-19 vaccine by the middle of September, anticipating full regulatory approval of a vaccine by then.

In a memo to service members, Defense Secretary Lloyd Austin said he would seek President Joe Biden’s approval to make the vaccines mandatory no later than mid-September or as soon as the Food and Drug Administration (FDA) gives final approval to the Pfizer vaccine, “whichever comes first.”

The memo urges troops to prepare for the requirement, and Austin added that if coronavirus infection rates rise, “I will not hesitate to act sooner or recommend a different course to the president if l feel the need to do so.”

Biden said in a statement Monday that he strongly supports Austin’s message, adding that “being vaccinated will enable our service members to stay healthy, to better protect their families, and to ensure that our force is ready to operate anywhere in the world.”

The announcement comes a week and a half after Biden set new rules requiring federal workers to provide proof of vaccination or face regular testing. At that time, Biden also directed the Pentagon to look into requiring the COVID-19 vaccine for members of the military.

The FDA is expected to give full regulatory approval to the Pfizer vaccine by next month. Without that approval, the Pentagon would need a waiver from the president to make the vaccine mandatory.

The decision to mandate the COVID-19 vaccine adds that inoculation to a list of other vaccines that service members are already required to receive.

Pentagon press secretary John Kirby said military services are being asked to develop plans to implement the mandate. He said the military did not have a deadline on which all troops should be vaccinated.

“Mandating vaccines in the military is not new,” said General Mark Milley, chairman of the Joint Chiefs of Staff, in a memo to the Joint Force on Monday. “Getting vaccinated against COVID-19 is a key force protection and readiness issue.”

U.S. Representative Mike Rogers, the ranking Republican on the House Armed Services Committee, said in a statement Monday, “We have already seen COVID-19 affect our readiness downrange. … We must not allow COVID-19 to be a hindrance on our force.”

According to the U.S. military, around half of the U.S. armed forces are fully vaccinated. The Air Force reports that more than 65% of its active-duty forces are at least partially vaccinated, while the Navy has the highest vaccination rates, with nearly 75% of all active duty and reserve sailors inoculated with at least one shot.

Once the vaccine is mandated, military officials say, a refusal can be punishable under the Uniform Code of Military Justice, according to The Associated Press.

Service members can seek an exemption from the vaccine mandate for health or religious reasons.

Source: Voice of America