BERLIN ? Germany's biggest-ever class action lawsuit began Tuesday, with over 34,000 plaintiffs seeking to overturn a law on keeping phone and Internet records which they say infringes their right to privacy.

Since 2008, German telecom firms have been obliged by law to keep a record of every email sent, every phone call made -- mobile or otherwise -- and all Internet usage as part of measures to prevent terrorism and fight crime.

They are not meant to record or listen to the phone calls or read the emails. All that is kept is who emailed or phoned whom, and which websites were visited; and to keep this log for six months for police to be able to consult.

Critics say that the potential for errors and abuse is huge, that a culture of excessive "Big Brother" surveillance is pervading other areas of life and that this and similar measures are being implemented in a ham-fisted manner.

The German constitutional court, which was not expected to take a decision on Tuesday, has in two previous rulings already forced the authorities to curtail the retention of data, known as "Vorratsdatenspeicherung."

Justice Minister Sabine Leutheusser-Schnarrenberger found herself in the unusual position of appearing both as plaintiff and defendant, having joined the action as a member of the opposition before becoming minister this year.