AUSTIN, Texas (AP) — Texas' Republican governor on Thursday told Defense Secretary Lloyd Austin that the state will not direct its National Guard members to comply with a Biden administration order requiring all members of the military to get vaccinated for COVID-19, as GOP opposition to the mandate grows.

Gov. Greg Abbott, who has become one of the nation's most outspoken governors in the rejection of vaccine mandates of any kind, told the Texas National Guard in October that its more than 20,000 members were included in his executive orders banning any governmental entity from imposing vaccine mandates.

RELATED: Gov. Abbott: Texas won't enforce Department of Defense's vaccine mandate on Texas National Guard

Texas has the largest National Guard contingent of any state and hasn't disclosed how many of its members are vaccinated.

Abbott's latest beef with the Biden administration came after five other GOP governors sent Austin a milder letter this week urging him to reconsider the requirements for Guard members on state active duty, when they are under their governor's orders but are still funded by the federal government.

Oklahoma's Republican governor has already sued the Defense Department over the vaccine mandate, and Abbott indicated that Texas could do the same.

"If unvaccinated guardsmen suffer any adverse consequences within the State of Texas, they will have only President Biden and his Administration to blame," Abbott said. 

Neither Abbott nor the Texas Guard immediately responded to inquiries about the number of vaccinated members. Pentagon officials also did not immediately respond to requests for comment.

Austin has said repeatedly that getting the vaccine is critical to maintaining a heathy, ready force that can be prepared to defend the nation. He decided that Guard members who refuse COVID-19 vaccinations will be barred from federally funded drills and training required to maintain their Guard status.

Army officials said Thursday that 98% of their active duty force had received at least one dose of the mandatory coronavirus vaccine. 

Thousands of members of the military are seeking exemptions or refusing the shots. But overall, the percentage of troops — particularly active duty members — who quickly got the shots exceeds the national average. According to the Centers for Disease Control and Prevention, about 72% of the U.S. population age 18 or older has gotten at least one shot. In Texas, about 70% of the population age 5 or older has been vaccinated, according to state data. 

Abbott has stationed more than 1,000 Guard members along the U.S.-Mexico border and given them the unusual power to arrest migrants on trespassing charges. In October, he extended a ban on vaccine mandates to private businesses under an executive order. However, the state's Republican-dominated Legislature did not approve a measure passing the prohibition into law.