OTTAWA - The opposition parties have united to drastically revamp the Conservative government's clean air legislation, making it virtually unrecognizable from its original form.

The new version forged by the opposition majority on the House of Commons environment committee includes a commitment to international carbon trading as called for by the Kyoto Protocol. Prime Minister Stephen Harper is vehemently opposed to that provision of the climate treaty.

When the Commons committee on Bill C-30 finishes its work, probably by the end of the week, the government's centrepiece environmental legislation will barely resemble the notions that emerged from the Conservative policy shops just a few months ago.

Whether the Conservative government accepts those changes when the legislation returns to the Commons or uses them to trigger an election call has become the subject of fevered speculation in Ottawa.

The opposition parties ended months of squabbling to unite after some bitter wrangling that pitted Liberals versus New Democrats and BQ members while the Conservatives enjoyed the spectre of a divided opposition.

What ultimately united opposition MPs was the desire to overhaul the government's legislation.

"What we're really doing here is rewriting the bill entirely," said Liberal environment critic David McGuinty, as the committee concluded a four-hour meeting on the legislation.

The revised bill will contain a commitment to international emissions carbon trading under the Kyoto Protocol. The government has rejected that as a scheme to send billions of taxpayers dollars abroad for Russian hot air.

It will provide for a "green investment bank" where companies that can't meet their targets will pay $30 per tonne penalties. The companies would be able to get the money back by achieving compliance within two years.

The opposition parties appeared on track to include a reaffirmation of the Kyoto emissions-reduction targets which the prime minister has repeatedly rejected as unachievable.

Conservative committee members raised numerous procedural questions as the committee pushed through clause-by-clause study.

"I think they're really trying to delay this so they can unleash an election and try to allege that all the opposition parties are trying to wreak economic havoc on the country," said McGuinty. "It will be a campaign of fear."

Time after time the beleaguered Conservative committee members were out-voted by the Liberals, New Democrats and Bloc Quebecois.

The revised bill will create a quandary for the prime minister since it contradicts some of his most forcefully stated positions on dealing with climate change.

The Tories have refused to say whether the vote on the revised bill will be deemed a confidence matter. If it is, the government could fall when the bill is passed.

There were some hints that the Conservatives might be softening in their opposition to the Kyoto Protocol. Brian Jean, representing Fort-McMurray-Athabaska, said he would not rule out a commitment to the Kyoto targets.

"The reality is ... there is a need to act right now and we need to look at all options to reduce greenhouse gases," he said.

But fellow Conservative Mark Warawa, parliamentary secretary to Environment Minister John Baird, said the party's opposition to the Kyoto targets has not changed.

NDP environment critic Nathan Cullen was ecstatic at the committee's progress. "In the last four hours there's been more movement on real changes than there has been in four months," he said.

Aaron Freeman of Environmental Defence said there is still a stark divide on the issue of Kyoto, but the opposition parties are working well together."We see some encouraging signs today."