A party official says Ichiro Ozawa and about 50 of his allies submitted their resignations from the Democratic Party of Japan on Monday. That is not enough to immediately end the ruling party's majority in the lower house of Parliament or force Noda out of office, though more could join later.
Ozawa helped bring the party to power in 2009. He has been a vocal critic of Noda's plan to double Japan's sales tax to 10 percent.
The tax hike passed the lower house, but needs to be approved by the less-powerful upper house.