Former Opposition Leader Malcolm Turnbull has crossed the floor during the vote on the Emissions Trading Scheme in the lower house of parliament.
Labor has at least one extra vote as the legislation setting up an emissions trading scheme moves through parliament's lower house today.
But Liberal MP Dennis Jensen, who was critical of Mr Turnbull's backing of legislation the coalition negotiated with Labor last year, said his former leader was "pretty much irrelevant now" on the issue.
The deposed Liberal leader has been the only opposition MP to speak in favour of the legislation during a lengthy debate.
The legislation faces defeat in the Senate where Labor lacks the numbers to win approval without the support of seven non-government senators.
"I'll be pleased if and when it's finally defeated in the Senate," Jensen told reporters.
"The problem is we all know which way it'll go in the house of reps, but the action is in the Senate."
