Importantly, Article 21(2) of the Constitution guarantees the secrecy of all means of communication, with limitations only allowed by legislation on public interest grounds. Article 4 of the Telecommunications Business Act, according to which the secrecy of communications handled by a telecommunications carrier shall not be violated, implements this confidentiality requirement at the level of statutory law. This has been interpreted as prohibiting the disclosure of communications information, except with the consent of users or if based on one of the explicit exemptions from criminal liability under the Penal Code (77).

Aside from these limitations for the exercise of public authority, business operators themselves are expected to check ("confirm") the necessity and "rationality" of the provision to a third party (99). This includes the question whether they are prevented by law from cooperating. Such conflicting legal obligations may in particular follow from confidentiality obligations such as Article 134 of the Penal Code (concerning the relationship between a doctor, lawyer, priest, etc. and his/her client). Also, "any person engaged in the telecommunication business shall, while in office, maintain the secrets of others that have come to be known with respect to communications being handled by the telecommunication carrier" (Article 4(2) of the Telecommunication Business Act). This obligation is backed-up by the sanction stipulated in Article 179 of the Telecommunication Business Act, according to which any person that has violated the secrecy of communications being handled by a telecommunications carrier shall be guilty of a criminal offence and punished by imprisonment with labour of up to two years, or to a fine of not more than one million yen (100). While this requirement is not absolute and in particular allows for measures infringing the secrecy of communications that constitute "justifiable acts" within the meaning of Article 35 of the Penal Code (101), this exception does not cover the response to non-compulsory requests by public authorities for the disclosure of electronic information pursuant to Article 197(2) of the CCP.