If Trudeau wins more seats than Scheer but falls short of a majority, as polls suggest could happen, he will need some opposition legislators to agree to help him govern. May’s price for such a deal could prove very high.

“We will not support any party or collection of parties to form a government that has not committed with real intent and clarity to move away from fossil fuels as quickly as possible,” she said.

She wants a ban on future crude oil pipelines and to block the planned expansion of the Trans Mountain Line from Alberta to British Columbia, which the Trudeau government bought for C$4.5 billion ($3.4 billion) last year.

Were the Liberals to need the support of Greens or the New Democrats, it would be “dire” for the oil industry, said Rafi Tahmazian, a portfolio manager specializing in energy investing at Canoe Financial in Calgary.