Following a decision this week to voluntarily block three pirate sites, Japanese ISP NTT has found itself in legal hot water. A lawyer, who is also an NTT customer, has filed a lawsuit against the provider, stating that in order to block sites the ISP must invade the privacy of its users' communications, something that is expressly banned under local law.

After hinting at moves to curb online piracy last month, on April 13 the Japanese government announced

emergency measures to target websites hosting pirated manga, anime and other types of content.

In common with dozens of counterparts around the world, the government said it favored site-blocking as the first line of defense. However, with no specific legislation to fall back on, authorities asked local ISPs if they’d come along for the ride voluntarily. On Monday, the Nippon Telegraph and Telephone Corp. (NTT) announced that it would.

“We have taken short-term emergency measures until legal systems on site-blocking are implemented,” NTT in a statement.

NTT Communications Corp., NTT Docomo Inc. and NTT Plala Inc., said they would target three sites highlighted by the government – Mangamura, AniTube! and MioMio – which together have a huge following in Japan.

The service providers added that at least in the short-term, they would prevent access to the sites using DNS blocking and would restrict access to other sites if requested to do so by the government. But, just a few days on, NTT is already facing problems.

Lawyer Yuichi Nakazawa has now launched legal action against NTT, demanding that the corporation immediately ends its site-blocking operations.

The complaint, filed at the Tokyo District Court, notes that the lawyer uses an Internet connection provided by NTT. Crucially, it also states that in order to block access to the sites in question, NTT would need to spy on customers’ Internet connections to find out if they’re trying to access the banned sites.

The lawyer informs TorrentFreak that the ISP’s decision prompted him into action.

“NTT’s decision was made arbitrarily on the site without any legal basis. No matter how legitimate the objective of copyright infringement is, it is very dangerous,” Nakazawa explains.

“I felt that ‘freedom,’ which is an important value of the Internet, was threatened. Actually, when the interruption of communications had begun, the company thought it would be impossible to reverse the situation, so I filed a lawsuit at this stage.”

Breaches of privacy could present a significant problem under Japanese law. The Telecommunications Business Act guarantees privacy of communications and prevents censorship, as does Article 21 of the Constitution.

“The secrecy of communications being handled by a telecommunications carrier shall not be violated,” the Telecommunications Business Act states, adding that “no communications being handled by a telecommunications carrier shall be censored.”

The Constitution is also clear, stating that “no censorship shall be maintained, nor shall the secrecy of any means of communication be violated.”

For his part, lawyer Yuichi Nakazawa is also concerned that his contract with the ISP is being breached.

“There is an Internet connection agreement between me and NTT. I am a customer of NTT. There is no provision in the contract between me and NTT to allow arbitrary interruption of communications,” he explains.

Nakazawa doesn’t appear to be against site-blocking per se, he’s just concerned that relevant laws and agreements are being broken.

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

The question of whether site-blocking does indeed represent an invasion of privacy will probably come down to how the ISP implements it and how that is interpreted by the courts.

A source familiar with the situation told TF that spying on user connections is clearly a problem but the deployment of an outer network firewall rule that simply prevents traffic passing through might be viewed differently.

Such a rule would provide no secret or private information that wasn’t already available to the ISP when the customer requested a banned site through a web browser, although it still falls foul of the “no censorship” requirements of both the Constitution and Telecommunications Business Act.

NTT Communications has declined to comment on the lawsuit but says it had no plans to backtrack on plans to block the sites. Earlier this week, SoftBank Corp., another ISP considering a blockade, expressed concerns that site-blocking has the potential to infringe secrecy of communications rules.