The broadcaster reported late on Saturday that most of the envelopes, postmarked Tokyo, had been delivered to companies based in Tokyo and Osaka, including two pharmaceutical firms, and one suspicious envelope had been received by a food company in the northern Japanese city of Sapporo.
Moreover, one of the messages demanded that the addressee pays 35 million won (over $31,200) in Bitcoin, otherwise threatening to spread cyanide-filled products.
The drug companies said that similar letters had been delivered to them last year and the police are trying to determine whether the two cases might be linked.
The broadcaster also noted that the name of a senior member of the Japanese doomsday cult Aum Shinrikyo (banned in Russia) is reported to have been mentioned on some of the letters.
Aum Shinrikyo, notorious for its 1995 Tokyo subway sarin attack, has been designated a terrorist organization and outlawed in some countries, including Russia.