Plenary sessions in the House of Representatives remain closed to the public even though the postwar Constitution stipulates otherwise.

For more than seven years — ever since the Sept. 11, 2001, terrorist attacks in the United States — the Diet's more powerful chamber has kept the doors shut to its full-dress meetings. Only visitors with an invitation from a lawmaker are permitted to watch the proceedings.

Reiko Oyama, a political science professor at Komazawa University in Tokyo, said enforcing restrictions on public attendance in the gallery for such a lengthy period on grounds of terrorism concerns appears to run counter to the Constitution.