Blair suffered a blow to his faltering domestic authority when 69 lawmakers from his party voted against key education reforms late on Tuesday. Further rebellion was expected in Wednesday's final vote.
The government easily won Tuesday's vote, but Blair was forced to rely on the support of the main opposition Conservative party to defeat an amendment.
"There are likely to be fewer rebellions than Tuesday, but we're sure that enough people will vote against to ensure that the Conservative votes are needed to carry the bill," said Labour lawmaker Jon Trickett.
In March, 52 of Labour's 353 lawmakers defied Blair to vote against the schooling plan, again leaving him needing opposition support.
"He's not the first prime minister to rely on opposition support, but this is within a year of being re-elected, a year in which he's suffered four defeats, won other votes by just one vote and needs the help of the Tories to get through his key legislation," said Philip Cowley, author of "The Rebels: How Blair Mislaid His Majority."
Cowley said more than 30 no votes or abstentions would be the largest in a third-reading vote since Blair took office in 1997; more than 37 would exceed the largest previous Labour rebellion, in 1947.
Opponents of the bill fear the new laws will give the private sector too much influence in schooling and create a two-tier system, with good schools getting better and weak ones getting worse, the AP reports.
Blair says his proposed changes are necessary to boost schools' standards and central to his vision of modernizing Britain's public services.
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