The Pentagon’s independent watchdog announced Thursday that it is launching a review into Secretary of Defense Pete Hegseth’s use of the messaging app Signal during group chats with top national security officials discussing military strikes against the Houthis.

Acting Inspector General Steven Stebbins revealed the review in a letter to Hegseth, stating that the evaluation was prompted by a request from the Chairman and Ranking Member of the Senate Armed Services Committee.

The lawmakers called for an investigation into Hegseth’s use of what Stebbins described as “an unclassified commercially available messaging application.”

“The objective of this evaluation is to determine the extent to which the Secretary of Defense and other DoD personnel complied with DoD policies and procedures for the use of a commercial messaging application for official business,” Stebbins said in the letter.

“Additionally, we will review compliance with classification and records retention requirements. We may revise the objective as the evaluation proceeds,” the letter adds. Both the White House and Hegseth himself have maintained that the information shared in the Signal chat was not classified.

In mid-March, The Atlantic’s Jeffrey Goldberg—known for his critical reporting on Donald Trump—revealed that he had been accidentally added to a national security group chat where top Trump officials were discussing airstrikes in Yemen.

The chat, active on March 15, included Defense Secretary Pete Hegseth, Vice President J.D. Vance, National Security Advisor Mike Waltz, Director of National Intelligence Tulsi Gabbard, and other senior members of Trump’s inner circle, as they deliberated potential strikes against the Houthis.