A lawyer sued a unit of Nippon Telegraph and Telephone Corp. on Thursday, demanding the network operator halt its plan to block access to websites that allow visitors to read pirated comics and books.

The lawyer, Yuichi Nakazawa from Saitama Prefecture near Tokyo, said in the first known such lawsuit that NTT Communications Corp.'s policy to block access to three sites providing hyperlinks to sites offering pirated publications is a violation of the secrecy of communications, which is banned by Telecommunications Business Act.

NTT said Monday it will block access to the websites in line with a recent government request. A government panel decided on a tentative plan earlier this month to address internet piracy, urging network operators to voluntarily cut off connections to such sites.

The move has raised concerns among legal scholars that such network access control could run afoul of Article 21 of the Constitution, which guarantees the secrecy of communication. The Telecommunications Business Act also obliges services providers to protect the secrecy of communications.

According to the complaint filed with the Tokyo District Court, Nakazawa, who uses an internet service provided by NTT Communications, claims that the provider will violate his secrecy of communications because it would need to know the content of customers' communications to block access to the sites.

The lawyer said NTT Communications' plan lacks ground as there is also no provision allowing it in the contract agreement.

"It is necessary to restrict sites of pirated publications but that does not mean you can do anything. We should have sufficient discussions for an appropriate measure, including revising the law," Nakazawa said.

NTT Communications declined to comment, saying it has not yet confirmed the complaint. It said there is no change in its plan to block access to the sites.