OTTAWA - Prime Minister Stephen Harper says it is constitutionally impossible for the government to comply with a newly passed law requiring Canada to respect its emissions-cutting commitments under the Kyoto Protocol.

Harper's remarks set the stage for a summer debate, and possibly a court challenge, over whether the government is flouting the will of Parliament.

The private members' bill, introduced by Liberal MP Pablo Rodriguez, gives the government 60 days to prepare a climate plan with measures to ensure that Canada meet its obligations under the Kyoto treaty. These include a six per cent cut in greenhouse gas emissions from 1990 levels by 2012.

Speaking shortly after the bill received royal assent, Harper suggested the bill is invalid because it is not a money bill, yet would involve large expenditures.

"There are strict constitutional limits which decide what you can do with such a bill," he said. "It could impose enormous costs on the Canadian government or on the economy. It's impossible constitutionally.

"This government has no intention of adopting measures that would be harmful to the Canadian economy and to jobs."

But Harper spokesman Dmitri Soudas later said the government was open to applying the bill if the Liberals would tell them how to do it.

"If the Liberals have a plan or a way to reach six per cent below 1990 on greenhouse gas reductions they should share that information with us so we can work together on achieving it."

The government has taken measures to cut greenhouse emissions, but not by nearly enough to meet the Kyoto target.

If the government fails to produce a Kyoto plan within six weeks, the government could be taken to court by citizens or the opposition parties, said Lorraine Weinrib, a professor of constitutional law at the University of Toronto.

In general a private members' bill is not supposed to impose financial obligations on the government, but the Commons Speaker Peter Milliken has ruled that the Rodriguez bill is not a money bill.

Kyoto advocates ay it would be possible to meet the treaty's targets without spending federal money, by introducing tough regulations or imposing a carbon tax.

"There are ways of doing this that wouldn't involve expenditure," said Weinrib. "The idea that the government has no obligation under this bill, which seems to be the comment the prime minister is putting out, that's hard to understand."

Harper cannot ignore the will of Parliament, said Stewart Elgie, a professor of environmental and constitutional law at the University of Ottawa.

"A fundamental principle of democracy is that ministers are not above the law in this country. The thing about this bill is, it ends the debate about whether Canada should comply with Kyoto. Parliament has said yes.

"It's up to cabinet to decide if they want to use regulations or spending or some other combination," he said. "They do not have the option of not complying with Kyoto."

The bill's passage is good news for Canadian democracy, he added. "It reaffirms that our elected representatives pass the laws in this country, even if the prime minister may not agree with them, and that's how a democracy is supposed to work."

Opposition Leader Stephane Dion said the Liberals will do all they can to make the government comply with the bill, but predicted real progress won't be made without a change of government.

He declined to say whether the Liberals would take the government to court.