Prime Minister Stephen Harper said he will not ignore a law passed Friday that requires the government to meet Kyoto's emission-reduction targets — but warned that he has no constitutional authority to implement it.

The bill — which gives the government 60 days to table a detailed plan outlining how Canada will reduce its greenhouse gas emissions — was introduced by Liberal backbencher MP Pablo Rodriguez and passed in the House of Commons in February, despite Conservative opposition.

The Liberal-dominated Senate passed the bill on Friday.

"I'm not saying I'm going to ignore it at all," the prime minister told reporters on Friday.

"But I don't believe that either the House of Commons or the Senate would want to force the government to do something that it doesn't have the constitutional authority to do."

Since the Conservatives came to power in January 2006, Harper has repeatedly said Canada's commitments under Kyoto — signed under a previous Liberal government — are not achievable by the 2012 deadline because it would devastate the economy.

Harper said Friday that the Speaker of the House has ruled the legislation is not a money bill — one that lays out government spending — so there are strict constitutional limitations in terms of what can be achieved.

"The bill cannot impose billions of dollars of costs on the government or on the Canadian economy," he told reporters.

Under the international Kyoto protocol, which was signed by Canada in 1998 and ratified in 2002, the country agreed to reduce greenhouse-gas emissions by six per cent from 1990 levels by 2012.

In an interview with the Canadian Press before the vote, Government House Leader Peter Van Loan also played down the significance of the Kyoto legislation.

"It's a very odd piece of legislation," he said, noting that it commits the government to achieving emission-reduction goals without spending a dime.

He added "there's some similarity" between the bill and a toothless motion passed years ago by Parliament to eliminate child poverty by 2000.

"Abstract goals like that are a tough thing to enforce as a law."

Liberal Leader Stéphane Dion said Harper should respect the legislation said he won't bring down the Conservative government over the issue.

"There are many, many things that I find wrong in this government. It's not a reason for me to say because these things are wrong, I'm ready to call an election," Dion said.

"At the end of the day this law will be helpful to see how the government is not doing the right thing."