Protests, legal challenges over aboriginal rights and the fate of an endangered population of killer whales are among the hurdles facing Kinder Morgan's Trans Mountain pipeline project.

When Prime Minister Justin Trudeau announced in Ottawa on Tuesday that cabinet had approved the $6.8-billion venture, it triggered a flurry of activity on the West Coast where legal teams were conferring with clients and protest groups were planning workshops.

Svenn Biggs, energy and climate campaigner for the environmental group Stand.earth, said the Trans Mountain decision "signals the beginning of a new phase in the struggle against pipelines."

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He said the fight will be waged on numerous fronts by groups that feel the project puts the environment at risk in British Columbia, violates the rights of First Nations and exacerbates climate change by promoting development of the Alberta oil sands for decades to come.

"You will see the movement continue to escalate in the streets as the number of protests and actions continue to grow, in the courts and at the ballot box," Mr. Biggs said.

The project will twin an existing pipeline that runs from Alberta to tidewater at a marine facility in Burnaby, B.C. The municipality already has a legal challenge under way.

"We've got limited power and we've tested every ability we have," said Burnaby Mayor Derek Corrigan, who has been adamantly opposed to the project from the start.

The city is expecting to hear a decision next week from an injunction application. That case seeks to halt preliminary planning work by the company, but Mr. Corrigan said if the application fails, there's not much the city can do beyond that.

"The only thing to be done is to leave it to the people," he said.

Mr. Corrigan plans to join public protests himself, but insists any demonstrations must not be violent.

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In Vancouver, neither the mayor, a city councillor most vocal about the pipeline issue, nor anyone from the Vision party was available to comment. Vancouver is in an awkward position on the pipeline issue because Vision councillors are also lobbying in Ottawa to get billions of dollars for transit and housing that are desperately needed in the city.

Rueben George, the manager of the Tsleil-Waututh First Nation sacred trust (a group dedicated to stopping the expansion) said there will be a quick consultation with the community in the next couple of days, but that he expects the band will be starting a legal challenge as well as holding rallies and protests.

"We are organizing things. We are calling our allies. We'll do what we have to," he said.

He said he expected to see strong protests, similar to the Standing Rock pipeline demonstrations now under way in North Dakota, but hopes it will not turn violent.

"That would be the last thing [Prime Minister Justin] Trudeau wants. That would be blood on his hands," he said.

There are seven legal challenges already before the courts and more are expected now that cabinet has approved the project.

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"Absolutely there are more challenges coming," Eugene Kung, staff counsel with West Coast Environmental Law said in an interview Wednesday. "If I was a betting man, I'd put a lot of money on that."

He said some First Nations were quick to challenge the National Energy Board process, which recommended approval in May, but others have been waiting to see what cabinet decided.

Mr. Kung said once Mr. Trudeau announced the project's approval, First Nations began calling to discuss their legal options.

"I've been fielding calls all day," he said.

Chris Tollefson, a law professor at the University of Victoria and director of Pacific Centre for Environmental Law and Litigation said there will be just as much legal opposition to Trans Mountain as there was to Enbridge's Northern Gateway project, which faced 18 court cases. The courts ruled the federal government had failed to adequately consult First Nations, and the project was in limbo when cabinet ruled Tuesday that it couldn't go ahead.

"We'll have to see what arguments are raised [about Trans Mountain] and what evidence is mounted, but the deficiencies with the process were so fundamental, deficiencies with the science and the technical record that was generated were so profound, that in my view there's a whole range of arguments that could be made," Mr. Tollefson said.

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Dyna Tuytel, a staff lawyer at Ecojustice, said one challenge that is already before the courts is over the NEB's decision not to consider the impacts of oil-tanker traffic on an endangered population of killer whales that live in southern Georgia Strait. That case focuses on the NEB process, but she said it will likely be expanded now to challenge cabinet's ruling.