Authorities did not identify the firm, but local media said it was major mobile carrier SoftBank Corp, a unit of the SoftBank Group. Police suspect Russian trade officials at Moscow's mission in Tokyo were involved in espionage, Jiji Press and other local media reported.
The reports added that the police have asked the Russian embassy to present two officials to the authorities. In a statement on its verified Facebook page, the Russian embassy described the media reports as "regrettable" and "cheap spy allegations".
SoftBank said in a statement that it is cooperating with the investigation and that "no information that is highly confidential - such as customers' personal information or anything that violates secrecy of communication" was compromised.