The National Police Agency revealed Friday that it plans to set up e-mail surveillance systems at the Tokyo Metropolitan Police Department and 13 other prefectural police headquarters in April.
The move will allow police authorities to access e-mail communications as part of their criminal investigations.
NPA officials said the surveillance systems are authorized under the wire-tapping law that went into effect in August last year.
According to the NPA, prefectural police authorities equipped with the surveillance system will require a court order before being allowed to monitor e-mail communications involving a crime suspect.
The surveillance device is plugged into the computer system of an e-mail service provider, with the system then automatically making a copy of all messages linked to the suspect's e-mail address.
Apart from the Tokyo Metropolitan Police Department, other prefectural police headquarters expected to receive the e-mail surveillance system are those in Hokkaido, Miyagi, Saitama, Chiba, Kanagawa, Shizuoka, Aichi, Kyoto, Osaka, Hyogo, Hiroshima, Kagawa and Fukuoka.
NPA officials are at pains to emphasize the growing importance of e-mail surveillance in criminal investigations, in addition to the surveillance of telephone conversations and fax communications.
Critics say, however, that great care should be taken to protect people's privacy.
Mizuho Fukushima, an Upper House member of the Social Democratic Party, said there will be no way of verifying whether the system has illegally retained digital records of e-mail communications that are not linked to crime suspects. Fukushima is calling for the establishment of a third-party body to monitor these activities and ensure there is no illegal wiretapping.
An NPA official said, however, that the system will automatically only make copies of messages sent to or received by designated addresses.