Matt Richtel notes in the New York Times Bits blog that the suit was filed on Tuesday. Part of the impetus was a story he wrote in 2005 that noted that it appeared the government was doing such tracking without "probable cause" making courts uneasy. The American Civil Liberties Union (ACLU) filed a Freedom of Information (FOI) request to gain information on how and how often the government tracked cell users. The Department of Justice did not provide an answer, which prompted the joint ACLU/Electronic Frontier Foundation (EFF) suit.