Support for the Trans Mountain pipeline expansion across Canada has dropped to its lowest levels in nearly two years, according to a new survey by the Angus Reid Institute.

The poll cites the growing price tag — which has ballooned from $5.4 billion to $12.6 billion — as the biggest cause for the deflating public support.

When first asked whether they were in favour of the pipeline, 55 per cent of respondents across Canada agreed. However, after being informed of the rising bill picked up by the taxpayer, that support dropped to 48 per cent.

Opposition to the project climbed from 38 per cent to 45 per cent when the cost was disclosed.

"We go from a pretty firm majority to quite a split," says David Korzinski, research director at Angus Reid.

"It's much closer when people, who might not have been aware, get that new cost estimate."

The expansion project would see the existing pipeline between Edmonton and Burnaby, B.C., twinned.

Opposition outweighs support in B.C.

In B.C., the new estimates meant that opposition was stronger than support for the first time since 2015, said Korzinski.

The poll found 48 per cent of British Columbians opposed the project compared to 50 per cent who supported it — but opposition jumped by four per cent when B.C. residents were informed of the new estimate.

An aerial photo of the Westridge Marine Terminal in Burnaby, B.C., the terminus of the Trans Mountain pipeline. (Jason Redmond/REUTERS)

The $12.6 billion construction cost figure includes $1.1 billion already spent on construction by Kinder Morgan, the previous owner of the project.

But it does not include the more than $4 billion the federal government spent to purchase the existing pipeline and the expansion plans, nor the $600 million reserve fund that Ottawa has set aside for contingencies.

Those sums bring the total cost of taxpayers' investment in the Trans Mountain expansion to more than $17 billion.