Environmental hearings into a proposed pipeline that would move bitumen from Alberta to British Columbia's coast began with heated words, as critics charged that Ottawa is trying to bully the project's opponents.

Enbridge Inc. wants to build the pipeline to carry oilsands-derived bitumen from a terminal near Edmonton, to a new supertanker port in B.C.'s Douglas Channel, where as many as 200 ships annually would take it for export to the U.S. and Asia.

While proponents contend the project would mean a significant economic boost -- a potential $3 trillion in economic development and more than 600,000 jobs -- opponents counter that the risk of an accident on the ecologically sensitive B.C. coastline is too high.

The hearings, which are expected to last for 18 months, got underway in Kitimat, B.C., on Tuesday. But as the two sides squared off, Enbridge announced that a possible gas leak was being probed at a well in the Gulf of Mexico, about 105 kilometres off the coast of Louisiana.

"A helicopter flyover was completed earlier today, and a three-foot (one-metres) diameter patch of bubbles has been spotted on the surface of the water in the vicinity of the Stingray natural gas pipeline," the Calgary-based company said in a release.

While a gas leak has a far different environmental impact than a potential oil leak, Enbridge has been forced to deal with a pair of U.S. leaks over the past two years that have undermined its claims of safety.

Earlier in the day, Haida leader Art Sterritt criticized Natural Resources Minister Joe Oliver, who warned in an open letter released Monday that environmentalists and other "radical" groups would hijack the regulatory panel hearings.

"We've got an Alberta prime minister trying to bully British Columbians," Sterritt said.

The anticipated $5.5-billion pipeline calls for the Alberta bitumen to be loaded onto supertankers for eventual export to Asia.

In his letter, Oliver wrote of opponents of the project: "Their goal is to stop any major project no matter what the cost to Canadian families in lost jobs and economic growth. No forestry. No mining. No oil. No gas. No more hydro-electric dams."

The minister subsequently clarified his position in an interview with CTV News Channel on Tuesday, saying that he wasn't referring to all environmentalists.

In particular, Oliver called out organizations that are "injecting money into Canada with the express purpose of delaying and ultimately defeating these big infrastructure projects."

Proponents of Northern Gateway have long argued the economic values of the proposed venture, which Oliver estimated will add billions to government coffers.

The twin pipeline, he added, would diversify Canada's resources to the Asia Pacific area.

"We need to diversify our markets and that's the strategic objective that a pipeline from Northern Alberta to the West Coast of British Columbia could achieve," he said.

The NDP's Associate Critic for Natural Resources has shot back at Oliver, accusing him of "bullying Canadians" with a letter on the eve of the hearings.

Kennedy Stewart said the minister's letter suggests that he doesn't respect the hearing process.

"He doesn't really have any plan for moving forward," said Stewart. "His only plan seems to be for China to stick a big straw into Alberta and suck all the oil out."

More than 4,300 groups and individuals have signed up to speak at the hearings designed to weigh potential impacts of the proposed 1,177-kilometre twin pipeline project.

Lifelong Kitimat resident Manny Arruda said Tuesday he would like the federal government to stay out of the proceedings, so local residents, who would live with the threat of an oil spill or other disaster, can make up their own minds about the project.

"I'm a northern person who lives in a northern British Columbia town who uses fuel and I don't consider myself an environmental activist," Arruda told The Canadian Press. "I take exception to that and I think we just want to get clear answers."

Arruda pointed out that Kitimat residents have embraced a plan for three liquefied natural gas plants in the region because they are believed to be safer for the environment.

The three-member panel comprised of biologist Sheila Legget, energy lawyer Kenneth Bateman and aboriginal geologist Hans Matthews will amass the evidence and then decide whether it's in the Canadian public interest and meets federal environmental safety regulations. Their verdict is expected in a report late in 2013.

In the past, Oliver has said that he wants the hearing process to adhere to a timeline to prevent it from going on for too long.

Stewart, however, said he doesn't think Oliver is encouraging the process but rather "bullying" Canadians.

"It's very disingenuous," he said. "It's almost un-Canadian for a minister to come out and start bullying people the day before this process starts."

Environmental groups have also taken issue with Oliver's suggestion that organizations backed by money donated by sources in the United States are somehow "radical."