British Columbia's Green party leader says they plan to use their increased political clout in the provincial legislature to fight Kinder Morgan's Trans Mountain pipeline expansion project.

Green Leader Andrew Weaver says they believe it's their responsibility to stop the federally-approved project that would triple the shipment capacity of Alberta oil products to British Columbia's coast.

Weaver says the Greens will seek intervener status to support mounting legal challenges by First Nations and municipalities opposed to the project.

When Alberta Premier Rachel Notley announced on Tuesday that her province had been given intervener status in the legal action, she said she believes one province or region can't hold hostage the economy of another province.

Weaver says B.C. Premier Christy Clark's support for the project was reckless.

Three Green members were elected to B.C.'s legislature last week and they are now in the position of wielding considerable political power in what could be a minority government after the final ballots are counted.