A group of House Republicans is demanding that Defense Secretary Lloyd Austin investigate "left-wing extremism" in the U.S. military.

Rep. Derrick Van Orden, R-Wis., himself a veteran, led five other GOP lawmakers in raising concerns related to the recent self-immolation of an active-duty Air Force member outside of the Israeli embassy.

"We write you today as members of Congress, many of us having served our country honorably, in our commitment to the security and integrity of our nation's armed forces. Your dedication to rooting out extremist behavior within our ranks has been well documented and demonstrates a commitment to maintaining the honor and cohesion of our armed forces," the Republicans wrote.

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"It is with this shared commitment in mind that we urge your attention toward the equally pressing issue of left-wing extremism among active-duty service members and veterans."

Their letter pointed out that the airman who lit himself on fire in February to protest Israel’s invasion of Gaza, Aaron Bushnell, was a self-declared "anarchist." They argued that his world view was "incompatible with that of our constitutional republic and entirely inappropriate for a member of the United States Military who had taken an oath to defend it at all costs."

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"This act, motivated by his stated desire to protest Israel in what he described as complicity in injustice, demonstrates the potential for ideologically driven behaviors to undermine the values, discipline, and safety of our military community, irrespective of the political orientation of those ideologies," Van Orden’s letter said.

The lawmakers pointed out multiple times that Austin has made combating extremism in the military a priority of his leadership.

In 2021, Austin established a working group on extremism in the military. He announced in April 2021 that it would be led by Bishop Garrison, the senior adviser to the secretary of defense on human capital and diversity, equity and inclusion.

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"Given your prior work in confronting extremism within the ranks, we are confident that you recognize the importance of a comprehensive approach to this challenge," they wrote.

"It is imperative that our efforts to identify and mitigate extremist influences encompass all forms of ideology that threaten the cohesion and effectiveness of our armed forces."

A Pentagon spokesperson told Fox News Digital when asked for comment on the letter, "As with all congressional correspondence, the Department will respond directly to the Members."