Politicians in Canada's parliament have voted, by 161 votes to 113, in favour of a motion that would force the government to meet its Kyoto targets.
The Kyoto agreement aimed to cut carbon emissions worldwide
Canada remains a signatory to the landmark international agreement to reduce greenhouse gases.
But the Conservatives have rejected most of the targets since forming a minority government in 2006.
The bill gives the government 60 days to table a detailed plan for getting in line with the Kyoto targets.
But the Conservative government has caused controversy by calling those targets unattainable and a threat to Canada's economy.
The new law is binding but Canada's Environment Minister, John Baird, has called the vote a stunt.
He has suggested the minority government might simply ignore it, essentially challenging the opposition to bring down the government and force a spring election.
Such a scenario would be unpopular with politicians across the political spectrum.
The vote comes after months of fierce debate between the Conservatives and the opposition Liberals over each other's environmental policies.
The Conservatives accuse the Liberals of doing very little to reduce greenhouse gases during the 12 years they were in power.
But the Conservative government has been on the defensive over its own record.
One environment minister has already lost her job over a series of mistakes, and an embarrassing letter written by the Canadian Prime Minister, Stephen Harper, in 2002 recently surfaced.
It derided the Kyoto accord as a socialist scheme designed to suck money out of rich countries.