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."