The Social Democratic Party may leave the three-party ruling bloc if U.S. Marine Corps Air Station Futenma remains in Okinawa as agreed to under a 2006 relocation accord between Tokyo and Washington, SDP President Mizuho Fukushima indicated Thursday.

If the pacifist party breaks with the coalition, it could destabilize the government because the ruling bloc, led by the Democratic Party of Japan, would lose its majority in the Upper House.

The SDP has five seats and the ruling bloc, not counting the SDP, has 120 seats in the 242-seat chamber.