“Stephen Harper continues to act as if this is 1948,” Mr. Mulcair told reporters outside of the House of Commons. “You can no longer force pipelines from the top down.” Calling oil tankers off the coast of British Columbia “madness,” Mr. Mulcair said that the decision was a “severe threat to social order, social peace.”

In the statement, Greg Rickford, the minister of natural resources, acknowledged that Enbridge’s efforts to win over British Columbia and native groups had fallen short. “The proponent clearly has more work to do in order to fulfill the public commitment it has made to engage with aboriginal groups and local communities.”

The president and chief of Enbridge, Al Monaco, seemed to agree during a conference call with reporters. “The economic benefits are not enough to secure public support,” he said.

The company must meet about 100 conditions imposed by the regulator before construction begins. Mr. Monaco declined to say how long that would delay construction, but he suggested at one point that it would take at least four years.

“We’re not going to be driven by our calendars or our watch here,” he said.

Northern Gateway has become something of backup for Canada, as approval for the Keystone XL pipeline remains mired in Washington. If built, Northern Gateway would ship about 500,000 barrels of bitumen a day to the coast compared with the 700,000-barrel-a-day capacity of Keystone XL, which would take oil sands production to the Gulf Coast of the United States. When Northern Gateway is combined with the country’s other pipeline plans, Canada could expand shipments from the oil sands by three million barrels a day.