TOKYO (AP) — A battle over an increase in Japan's sales tax is threatening to split the ruling party and weaken Prime Minister Yoshihiko Noda's hold on power.

The tax hike is expected to come before Parliament on Tuesday, but media reports Monday say more than 50 ruling party lawmakers plan to vote against it. That would not be enough to kill the bill, because it also has opposition party backing.

But the reports said dozens are also considering leaving the ruling party altogether. If 54 or more do so, Noda's party would lose its majority in Parliament's lower house and he would be vulnerable to a no-confidence vote.

Noda has said he's ready to stake his career on the tax bill, which he says is needed to fight Japan's swelling national debt.