OTTAWA — In a decision that will almost surely prompt showdowns with environmentalists, indigenous groups and some political allies, Prime Minister Justin Trudeau of Canada approved on Tuesday the expansion of a pipeline linking the oil sands in Alberta to a tanker port in British Columbia.

The Kinder Morgan Trans Mountain project will increase the capacity of a 53-year-old pipeline to 890,000 barrels a day from 300,000 and expand the tanker port. In recent weeks, there have been several large protests against the project, particularly in Vancouver, British Columbia. But Rachel Notley, the premier of Alberta, has repeatedly said that the project is critical to the future of her province’s energy industry.

Environmental groups began condemning the decision as Mr. Trudeau was making his announcement late Tuesday afternoon, but the prime minister said that the pipeline expansion did not contradict his pledges to improve environmental protection and mitigate climate change.

“We’ve heard clearly from Canadians that they don’t want to see someone trying to make a choice between what’s good for the environment and what’s good for the economy,” Mr. Trudeau said at a news conference. “They need to go together, and the decisions we’ve made today and leading up to today are entirely consistent with that.”