The FBI sought interviews with six Democratic lawmakers who appeared in a video urging U.S. service members to reject “illegal orders,” a development that suggests a rapidly escalating review of the lawmakers’ conduct that some military and legal experts say could prove difficult to prosecute under existing statutes.

The FBI and Justice Department contacted the House and Senate sergeants-at-arms on Monday to begin scheduling conversations with the lawmakers following the release of the video last week, according to a statement released by the six Democrats involved in making the now-infamous video. Trump administration officials, including War Secretary Pete Hegseth, have dubbed the group the “Seditious Six.”