The American Civil Liberties Union (ACLU) and the Electronic Frontier Foundation are suing the US Department of Justice over its ability to track individuals via their mobile phones.

The two groups submitted a Freedom of Information request to the DoJ in November 2007, after reports that law enforcement agencies had been using mobile phones to track individuals without obtaining a warrant.

"This is a critical opportunity to shed much-needed light on possibly unconstitutional government surveillance techniques," said Catherine Crump, staff attorney at the ACLU and lead attorney on the case.

"Signing up for cellphone services should not be synonymous with signing up to be spied on and tracked by the government."

The case arose after law enforcement officials told some media outlets that they could track people without needing warrants as mobile phone companies were handing over user information as a matter of course.

"The public has an overwhelming interest in the requested information, which concerns our most personal communications," said David L. Sobel, senior counsel at the Electronic Frontier Foundation and co-counsel on the case.

"But remarkably, the Justice Department refused to respond quickly to the request, as the law requires when 'urgent' information is at issue. Further delay will allow important privacy policies to be developed behind closed doors. "

Tracking an individual's location via their mobile phone is relatively easy using cell triangulation.

The phone automatically identifies itself to mobile base stations in the area when switched on. By measuring the distance between multiple stations, the user's location can be identified.

Law enforcement is becoming increasingly adept at using technology in investigations.

A case in 2006 against mafia member John 'Buster' Ardito revealed that the FBI was able to activate the microphone in Ardito's mobile phone and use it to surreptitiously record his meetings.