Texas Governor Greg Abbot has announced a lawsuit against the Biden administration, challenging a Covid-19 vaccine mandate for National Guardsmen, whom he argues are under the state’s authority.

In a letter to Major General Tracy Norris, adjutant general of the Texas Military Department, Abbott said on Tuesday that he had issued an order saying no member of the National Guard in the state will be “punished” for choosing not to get a vaccine, despite recent mandates that have led to numerous military service members losing their jobs.

Abbott has been clear in refusing to impose a vaccine mandate on his state’s military for weeks now, even in light of a Pentagon mandate put in place in August. Army National Guard members still have until June 30 to be vaccinated.

Several governors have opposed the White House on the question of authority over National Guard members. Oklahoma Governor Kevin Stitt launched a lawsuit that ultimately failed, also seeking to block mandates for the Guard.

According to Abbott, he is the commander-in-chief of the Texas National Guard and he holds ultimate authority over them, thanks to Title 32 of the US Code, which dictates that Guard members are under state authority unless called upon on federal orders, typically for an overseas deployment or national emergency.

Under Title 10, President Joe Biden can put the Guard members under federal orders, but they would still ultimately fall back under state control when those orders are completed. This leaves vaccine mandates in a legal gray area, as a military vaccine mandate would mean National Guard soldiers cannot be called upon for federal orders, should a challenge like Abbott’s prove successful. It could also mean, however, that National Guard soldiers would be required to be vaccinated against Covid-19 should their unit receive federal orders, which would see Abbott's challenge simply stall the mandate if successful.

While Abbott admits in his letter that his efforts could fail, he argued that federal courts will be forced to decide whether Biden “violated” the law by “undermining” the governor’s alleged authority with the mandate.