The mayor of Calgary has slammed the B.C. premier, the mayor of Vancouver and a former U.S. vice-president over opposition to Kinder Morgan's Trans Mountain Pipeline expansion — and he's not mincing words.

"It's very clear that Mr. [John] Horgan, who I think is one of the worst politicians that we have seen in Canada in decades, appeals to populism in a way that is not based on fact," Naheed Nenshi said Friday.

Nenshi was responding to a tweet by Al Gore, former U.S. vice-president and climate change activist, criticizing the expansion and showing solidarity with Horgan and Vancouver Mayor Gregor Robertson.

"The Kinder Morgan pipeline carrying dirty tar sands oil would be a step backward in our efforts to solve the climate crisis. I stand with @jjhorgan, @MayorGregor, and all of the Canadians — including the First Nations — who are fighting to stop this destructive pipeline. #StopKM," Gore tweeted Thursday.

The Kinder Morgan pipeline carrying dirty tar sands oil would be a step backward in our efforts to solve the climate crisis. I stand with <a href="https://twitter.com/jjhorgan?ref_src=twsrc%5Etfw">@jjhorgan</a>, <a href="https://twitter.com/MayorGregor?ref_src=twsrc%5Etfw">@MayorGregor</a>, and all of the Canadians - including the First Nations - who are fighting to stop this destructive pipeline. <a href="https://twitter.com/hashtag/StopKM?src=hash&ref_src=twsrc%5Etfw">#StopKM</a> —@algore

"Last I checked, Mr. Gore has no regulatory authority in Canada, nor, obviously from that tweet, any actual knowledge of the situation. So it's a shame that someone like that would comment on something they obviously don't understand," Nenshi said.

Nenshi says support for Trans Mountain is growing despite what the Vancouver mayor has said.

"As much as I respect Mayor Gregor Robertson, we don't operate by mob rule here," Nenshi said.

Earlier this week, Robertson suggested that protesters would probably prevent construction of the pipeline.

"When governments have conducted their regulatory work, when the approvals and processes have gone through, a few loud people lying in front of bulldozers don't stop [development] in this country. That's mob rule. We have to abide by process here and by democracy here and that's exactly what has been done."