The Supreme Court heard oral arguments Monday in a case that will determine whether three Muslim men from California can sue the FBI for illegally spying on them after the 9/11 attacks. Lawyers for the bureau argue the suit should be dismissed under the “state secrets” privilege.

In 2006 and ’07, the FBI recruited a man named Craig Monteilh to pose as a Muslim convert in order to infiltrate mosques and Islamic groups around Orange County, where he secretly recorded conversations. The former imam at one mosque, Sheikh Yassir Fazaga, who is now lead plaintiff in the lawsuit, says Monteilh planted a recording device in his office.

Sheikh Yassir Fazaga: “And to me, that’s a very, very sensitive area. I am a therapist, where people come in, and they share their issues with me. But to know that the FBI potentially was recording these sessions, that is illegal, it is unethical, it is not constitutional, and it puts a lot of people’s lives in jeopardy, and their well-being and their rights of privacy.”