Mr Turnbull, who is fearful of giving Labor a trigger for an early election, hinted yesterday at moving amendments to Labor's emissions trading scheme when the Senate voted on it next month, rather than opposing it outright, as is the Coalition's current intention.

The Nationals would oppose any such move and senior Liberals cautioned it would worsen the split in their ranks.

Mr Turnbull told ABC radio yesterday there were "powerful arguments" for delaying the scheme until next year, after the United Nations summit in Copenhagen in December, and by which time the final shape of an emissions trading scheme in the United States should be known.

But he accepted the Government was driving the agenda and business was pushing the Coalition to have some influence in shaping the scheme.

"What they're saying is we should - even though the Government is not proceeding as prudently as they should in terms of timing - we should nonetheless seek to make this law better so that it is more environmentally effective and less economically damaging," he said.

"There's an overwhelming consensus that the law should be changed and we should seek to advance and promote those changes."

But the proposal rang alarm bells, one senior Liberal saying the party room had agreed to oppose the bill on August 13, when the vote is scheduled.

Should the Government reintroduce the bill three months later, thus setting it up as a trigger for an early double dissolution election, the Coalition would decide tactics then.

"He's floating the proposal that we might change our approach and move amendments to the bill in August," the Liberal said.

"He'd have to get the shadow cabinet and the party room to agree to a set of amendments. That will be a challenge. What's uniting everybody is to vote this bill down in August."