Some Republican Senators and governors are continuing their pushback against the military’s COVID-19 vaccine mandate, and it could be the next hurdle for the 2023 National Defense Authorization Act, which lawmakers hope to pass this month, as The Hill reported.

“The Biden vaccine mandate on our military creates a national security risk that severely impacts our defense capabilities abroad and our state readiness here at home,” 21 Republican governors wrote in a Wednesday letter, led by Gov. Bill Lee (R-Tenn.). “Current service members are leaving our ranks, and new recruits are not signing up to join.”

In another letter dated Wednesday, 13 Republican Senators wrote that “the effects of the mandate are antithetical to readiness of our force, and the policy must be revoked.”

The House passed a defense authorization bill this summer, but authorization bill never passed the Senate. The two chambers’ Armed Services leaders are working on a compromise bill they hope can pass both bodies and get President Biden’s signature by the end of the calendar year.

National Guard photo of Gov. Lee by Staff Sgt. Timothy Cordeiro