Tokyo ( CNN ) -- Fifty rebel lawmakers resigned Monday from Japan 's governing party , weakening the majority of Prime Minister Yoshihiko Noda as he pushes a controversial increase in the sales tax through parliament . Led by the influential Ichiro Ozawa , 40 members of the lower house and 12 members of the upper house have left the Democratic Party of Japan , said Kenji Yamaoka , a senior lawmaker allied with Ozawa . However , two of the lower house lawmakers on the list announced by Yamaoka -- Megumu Tsuji and Takeshi Shina -- subsequently said they were not leaving the party , their offices said . The exodus is in protest over Noda 's plan to double the sales tax from 5 % to 10 % to try to tackle Japan 's huge public debt , Yamaoka said . The lower house passed the measure last week despite opposition from the group led by Ozawa , a former party leader known for his political power-broking . The departures Monday whittle down Noda 's majority in the lower house , leaving the Democratic Party of Japan with 251 out of 480 seats . In the upper house , which is still to vote on the sales tax legislation , the party now holds 92 out of 242 seats . Noda , who took office in September , is the latest in a string of politically fragile Japanese leaders . He is the sixth prime minister in the six years since the departure of Junichiro Koizumi , who was in power for more than five years . The Ozawa-led exodus has fueled speculation about a possible vote of no confidence being introduced against Noda . But Ozawa has so far failed to lure away enough Democratic Party of Japan members to threaten Noda immediately . If a vote of no confidence were to be called and Noda lost , he would have to step down or call a snap election . Ozawa said last week that he expected a general election could be called `` in the near future . ''
NEW : Two of the Japanese lawmakers on the list of those leaving say they are staying . The departing parliamentarians are led by the influential Ichiro Ozawa . They say they are protesting the prime minister 's plan to double the sales tax . It leaves the government with 251 out of 480 seats in the lower house .