(The Hill) — Virginia Gov. Glenn Youngkin (R) urged Defense Secretary Lloyd Austin to “indefinitely postpone” the implementation of the department’s coronavirus vaccine mandate for Army National Guard Troops in a new letter obtained by The Hill on Tuesday.

The letter, which was also signed by Republican Virginia Reps. Bob Good, Rob Whittman, Ben Cline and Morgan Griffith, argues that the mandate will drive members of Virginia’s national guard away.

“This directive will unnecessarily impact troop readiness, at a time when the Virginia National Guard has substantial deployments and as our nation enters hurricane season. These guardsmen deserve the opportunity to continue to serve, and we need them,” the letter reads.

Additionally, the letter cites recently dropped mask and vaccine mandate in other jurisdictions, natural immunity to the virus, and the use of therapeutics as reasons for dropping the mandate.

“We know you share our great appreciation and respect for the brave men and women of our National Guard. Their service and sacrifice reflect their commitment to our country and the principles embodied in our nation,” the letter concludes. “A select number of them have made a decision not to get vaccinated and whether that decision is based on sincerely held religious beliefs, their own medical choices, or another matter of conscience, our nation should respect and accommodate it.”

Other Republican governors, including Texas Gov. Greg Abbott (R) and Oklahoma Gov. Kevin Stitt (R), have also voiced objections to the vaccine mandate for the National Guard.

Austin has argued that as defense secretary, he has the authority to set medical requirements.

The letter is the latest effort from Republicans to urge Austin to do away with the mandate. Soldiers in the Army Reserve and Army National Guard have until Thursday to receive the vaccine or get an exemption. If they do neither, they could face punishment or removal from service.

Roughly 60,000 Army Reserve and National Guard soldiers are still unvaccinated against COVID-19. According to the Military Times, 3,400 troops have been involuntarily separated from service for refusing to get the shot.