The Pentagon says it is investigating Democratic Sen. Mark Kelly of Arizona for possible breaches of military law after Kelly joined a handful of other lawmakers in a video that called for U.S. troops to refuse unlawful orders.

The Pentagon’s statement, which was posted on social media on Monday, cited a federal law that allows retired service members to be recalled to active duty on orders of the defense secretary for possible court-martial or other measures. Kelly served in the U.S. Navy as a fighter pilot before going on to become an astronaut. He retired at the rank of captain.

It is extraordinary for the Pentagon, which until the second Trump term has usually gone out of its way to act and appear apolitical, to directly threaten a sitting member of Congress with investigation.