A Democratic senator who has long called for Congress to take a more active role in decisions to authorize U.S. military action around the world is expressing concern about the Trump administration’s view of “collective self-defense.”

Virginia Democratic Sen. Tim Kaine released a letter Wednesday to Defense Secretary James Mattis indicating that there are very few limits on the scope of self-defense under interpretations of current law.

“The collective self-defense supplemental rule of engagement, when approved, permits U.S. forces to defend partner forces from attack or an imminent threat of attack with necessary and appropriate force, and typically the authority applies irrespective of the group or individual committing the hostile act, or demonstrating hostile intent,” the Defense Department said in a reply to Kaine about previous questions, according to Kaine’s letter.

“As such, collective self-defense is not typically limited to particular groups or individuals committing the hostile act or demonstrating hostile intent, including not being limited to groups covered by the 2001 AUMF or other congressional authorizations for the use of force,” the reply to Kaine said, much of which appears to remain classified.

“I am alarmed that the Department of Defense believes that, by merely designating a group as a partner force, it can respond with military action to protect that partner force and its property if threatened by any group — even one that poses no direct threat to the United States, its Armed Forces or persons, nor is covered by an AUMF,” Kaine wrote in his Wednesday letter.