Alberta Premier Rachel Notley says she will not ask Tzeporah Berman to step down from the government's Oil Sands Advisory Group over her opposition to the Kinder Morgan pipeline.

"The answer to that is no," Notley told reporters Wednesday on a conference call from Ottawa.

"I think we need diverse voices there, and she is participating in a process which, quite frankly, is separate from pipeline approval, in that they don't make decisions around pipeline approval."

The federal cabinet's decision to approve Kinder Morgan's Trans Mountain pipeline expansion was hailed by Notley on Tuesday as a great move for Alberta.

Shortly afterwards, Berman retweeted a post by Vancouver Mayor Gregor Robertson opposing the decision, then added some tweets of her own.

"Justifying Kinder Morgan and Line 3 because of Alberta Emissions Cap ignores First Nations treaty rights and their serious environmental impacts," Berman wrote.

"Supporting the Alberta Climate Plan, which I do and working to implement it, doesn't mean support for every pipeline proposal."

The OSAG is advising the province on how to implement a new 100 megatonne annual cap on carbon from the oilsands.

The appointment of the environmental activist as the group's co-chair in July was controversial from the start.

Earlier this year, Berman got into hot water for likening the oilsands to Mordor, a dark, scorched land of suffering in the Lord of the Rings trilogy

Opposition politicians are now calling for the premier to drop Berman from the advisory group based on these latest tweets. Notley said that won't happen.

"We're not about kicking people off of things when they express opposition," she said. "(Berman is) working at this point effectively in the job we've asked her to do, and as long as that continues then she will stay there."

Berman not only adviser opposed to pipeline

Berman isn't the only member of the advisory group to express opposition to Trans Mountain.

In an opinion piece published this week in the Vancouver Sun, Karen Mahon, the Canadian national director of Stand.earth, formerly known as ForestEthics, predicted Trans Mountain will never be built because mass protests and lawsuits will hold it up.

"The world doesn't need this pipeline," Mahon wrote. "We need energy solutions that move us toward the sustainable energy economy, not away from it."

Wildrose Leader Brian Jean said Notley needs to reprimand and fire Berman and Mahon, and a third member of advisory group, Tim Gray, the executive director of Environmental Defence.

Jean said Environmental Defence sent an email Wednesday vowing to stop the Energy East pipeline from ever being built.

"Premier Rachel Notley can't have her chief oilsands advisors publicly declaring war on several important pipeline projects Alberta needs built," Jean said in a news release.

"It's clear, the NDP has failed to receive their so-called 'social licence' with these individuals, despite bringing in the largest tax increase in Alberta history. They need to go or premier Notley needs to denounce their work attacking Alberta's energy sector."

The $6.8-billion Trans Mountain pipeline expansion is expected to create 15,000 jobs. The twinned line will take oil products from the Edmonton area to Burnaby, B.C., where they can be shipped to markets overseas.

Since she took office in May 2015, Notley has advocated for a pipeline that can get Alberta oil to Asia, where it can fetch world prices and break the province's dependence on the United States as its only market.