Ontario Tory MP Leona Alleslev, who was elected as a Liberal in 2015 but crossed the floor in dramatic fashion last month, rose in question period to ask why Canada is pricing carbon when its emissions are a drop in the bucket compared to China and the United States.

The Liberal parliamentary secretary tasked with defending the government's carbon pricing plan had a sharp retort Monday for a former teammate who bolted to the Conservatives.

Alleslev received some jeers when she stated in her preamble that "we all agree that climate change needs to be addressed." Liberals have been pressing the Tories to release their own climate plan.

Nova Scotia MP Sean Fraser, who often pinch hits for Environment Minister Catherine McKenna in question period, sparked laughs with his response.

"If the honourable member honestly believes all members of this House [on the Conservative benches] believe this is a threat that needs to be challenged, I suggest she hasn't been with them quite long enough," Fraser said.

The Liberal MP added that "anybody who wants to join us for the next campaign, who believes this message, would be welcome on this side of the House."