OTTAWA - The government's centrepiece environmental legislation, the Clean Air Act, is in deep trouble and there's speculation it could become the trigger for an election.

This week all three opposition parties proposed amendments to the bill -- amendments that would enshrine the emissions-cutting targets of the Kyoto Protocol, which the Conservatives have called unachievable.

After the amendments were tabled, the government cancelled a Tuesday meeting of the committee studying the bill.

Environmentalists were delighted at the unusual consensus among the New Democrats, Bloc Quebecois and Liberals, whose amendments coincide on key points such as firm limits -- known as hard caps -- for greenhouse gas emissions in line with the Kyoto targets.

"Obviously I'm ecstatic,'' said Dale Marshall of the David Suzuki Foundation. "We weren't sure we would get this level of commitment and consistency.''

Since the three opposition parties can outvote the Conservatives, it appears the bill will be sent back to the Commons with Kyoto targets written in, leaving the government with a political conundrum.

Some have speculated that Prime Minister Stephen Harper could declare the bill a matter of confidence and call an election after losing a vote on the opposition amendments.

The argument is that the Conservatives are geared up for an election, at a level of mobilization that would be difficult to sustain for long, and Harper is looking for a trigger.

But opposition critics say the Conservatives would be foolhardy to pick an electoral fight on the environment, given their lack of an overall plan for addressing climate change.

"If Mr. Harper would like to fight the next election ... on our commitment to Kyoto and his commitment to nothing, we'll gladly join him in that debate,'' said NDP environment critic Nathan Cullen.

The government could decide not to proclaim the revised Clean Air Act into law, but that would leave a gaping hole in its environmental platform when environment is a top issue in the polls.

Liberal environment critic David McGuinty called on the Conservatives to recognize that their policy to date has been wrong, and accept the Kyoto targets.

"I think the government should grow a set of shoulders, and admit to Canadians that they're fundamentally wrong on climate change,'' he said.

"They ought to say, `We made a mistake with this Clean Air Act, it was dead on arrival. Now we've got to put Humpty Dumpty together.'

"I think the government should simply say, `We're going to abide by the will of Parliament.'''

But Conservative opposition to the Kyoto targets has been hammered home forcefully over many months, and many consider a reversal unthinkable.

"I don't think it's in their DNA,'' said Cullen.

Environment Minister John Baird gave few hints about the government's strategy when questioned Tuesday. He said he is still reviewing the opposition amendments.

He insisted the government has a solid climate plan, citing numerous recent announcements of funding for the provinces under the ecoTrust fund. Baird declined to speculate on whether the government would be prepared to fight an election on the Clean Air Act.

Proposed amendments by the three opposition parties not only agree on the Kyoto target, a six per cent cut in greenhouse emissions from 1990 levels by 2012, but also on subsequent targets: a 25 per cent cut by 2020 and an 80 per cent cut by 2050.

The bill as it stands includes no reference to Kyoto and cites only one target, a 40-to-60 per cent emissions cut by 2050.

Any of the parties can introduce further amendments, and there could be horse-trading in the committee, but time is limited: it must report back to the Commons by March 30.

None of the opposition parties has shown any hint of backing down on the Kyoto issue. Asked whether his party is committed to the treaty, Bloc Quebecois Leader Gilles Duceppe replied: "Absolutely.''