A Justice Department lawyer on Monday urged a federal judge in Washington to throw out a suit that challenges the government’s alleged secretive effort to assassinate a radical cleric reportedly hiding in Yemen.

The American Civil Liberties Union brought the suit in August on behalf of the father of cleric Anwar al-Aulaqi, a U.S. citizen the federal government has designated a global terrorist and a leader of Al-Qaida in the Arabian Peninsula. Lawyers for al-Aulaqi’s father, Nasser al-Aulaqi, are seeking an injunction to block the government from killing Anwar al-Aulaqi. The attorneys argue that a person targeted for assassination has due process rights to challenge his designation on the list.