Subsidiaries NTT Communications, NTT Docomo, and NTT Plala will continue the measure until the Japanese government is able to establish new legislation regarding site-blocking.
The Japanese government officially asked Internet service providers in Japan to block access to pirated manga websites on April 13.
The government had stated earlier this month that it planned to officially ask the providers to block the sites.
Nippon Telegraph and Telephone Corporation (NTT) announced on Monday that it will begin blocking three websites with pirated content as a “short-term emergency measure” after preparations are complete.