Environment Minister Catherine McKenna spent much of the first question period of the fall in the House of Commons defending the Liberals' plan to impose a carbon price on any province that doesn't come up with its own.

McKenna discussed imposing a national carbon price Sunday in an interview with CTV's Question Period. She also said the government won't toughen the carbon emission reduction targets set by the previous Conservative government, which were widely thought to be too lenient.

Those two assertions put her solidly between the two opposition parties, with the Conservatives attacking over the threatened carbon price, and the NDP demanding stronger action to reduce carbon emissions.

The Conservatives accused the Liberal government of preparing to raise costs for Canadians through a carbon tax or cap and trade system, something McKenna has been trying to negotiate with the provinces since last fall in a bid to lower Canada's carbon emissions. A carbon tax, the Conservatives say, will hurt the economy in western Canada, which is already suffering under low oil prices.

Conservative MP Jason Kenney, who is running to be leader of the Alberta PCs, said a carbon tax would increase the cost of gasoline as well as home-heating fuel.

McKenna suggested Kenney was ignoring the free-market argument for a carbon price, which is that raising the cost forces consumers to lower their use and encourages companies to innovate to save money.

"But perhaps he doesn't believe in climate change and that might be the problem," she said.

New Democrat Leader Tom Mulcair said the Liberals were breaking their promise on carbon emissions. "Does the minister think that's change, serving up the Conservatives' plan with a smile?" he said.

McKenna said Canadian emissions went up while the Conservatives were in office, making the targets tougher to hit.

"Let's be clear. The Harper targets were fake targets," she said. "We are going to deliver real action," she said.