The lawsuits will name Malaysian state oil firm Petroliam Nasional Berhad (Petronas), which owns a majority stake in the project, as an associated party, representatives of the aboriginal and environmental groups told Reuters this week.
Canada in September gave the green light for the Pacific NorthWest LNG project in northern British Columbia with 190 conditions, despite concerns it would destroy a critical salmon habitat and produce a large amount of greenhouse gases.
The decision was a major test for Canada's Liberal Party, juggling the needs of an energy industry suffering from job losses and the concerns of environmentalists, who were courted by Prime Minister Justin Trudeau in last year's election campaign.
The groups will file the lawsuits at the Federal Court in Vancouver. The legal challenge puts the future of the project at risk after it has already been hit with a three-year delay in getting its environmental permit and as Asian LNG prices have dropped by about two-thirds since 2014.
The Canadian government was not available for immediate comment outside regular business hours. Petronas did not immediately respond to a request for comment.
"We believe there are serious flaws in the environment assessment process," said Greg Knox, executive director of SkeenaWild, an environmental group filing one of the lawsuits.