VANCOUVER - The Federal Court of Appeal has allowed six challenges of the Trans Mountain pipeline expansion focusing on Indigenous consultation to proceed, while dismissing several claims centred on environmental concerns.

The decision calls for narrowly focused, expedited court proceedings that will only examine the quality of the federal government's consultation with Indigenous communities between August 2018 and June 2019.

"Many of the Indigenous and First Nation applicants now allege that the poor quality and hurried nature of this further consultation rendered it inadequate," says Justice David Stratas in a decision released Wednesday.

The Trudeau government has twice approved a plan to triple the capacity of an existing pipeline from Alberta's oilpatch to a terminal in Burnaby, B.C.

The Federal Court of Appeal tore up the original approval last year, citing both an insufficient environmental review and inadequate Indigenous consultations. The Liberals say they fixed both problems and approved the expansion a second time in June.

Three environmental groups, eight First Nations and the City of Vancouver sought leave to appeal. Conservation groups argued there were inadequate protections for endangered species affected by increased tanker traffic, while several First Nations said the government came into the most recent discussions having predetermined the outcome.

The court has allowed requests to appeal by the Coldwater Indian Band, Squamish Nation, Tsleil-Waututh Nation and Upper Nicola Band, the Stk'emlupsemc Te Secwepemc and a coalition of First Nations in B.C.'s Fraser Valley.

Stratas explains in his ruling that decisions to grant leave to appeal are based on whether arguments are "fairly arguable," meaning any claims with fatal legal errors must be dismissed.

There are two sets of arguments advanced by First Nations that don't meet the "fairly arguable" standard, including any assertion of a right to veto as well as issues already decided by the court's first ruling last August, Stratas says.

The federal government engaged in additional consultations after the ruling and the court should rule on whether those talks were adequate, he says.

However, Stratas says applicants' arguments on environmental issues aren't fairly arguable. Many were already dealt with or could have been raised during the court's first hearing on the project, he says.

In its first ruling, the court called for a new National Energy Board review focusing on marine impacts and the review was completed in February. The board submitted a "comprehensive, detail-laden, 678-page report" to the government, Stratas notes.

Though many applicants say the new report is deeply flawed, this argument "cannot possibly succeed" based on the degree of examination and study of marine shipping and related environmental issues in the new report, he says.

The federal government bought the existing pipeline and the unfinished expansion work for $4.5 billion last year, promising to get it past the political opposition that had scared off Kinder Morgan Canada from proceeding.

Stratas rejected arguments that alleged the government made a biased decision to approve the project because it is the owner.

He says the Governor in Council, which represents the Crown and acts on the advice of cabinet, is actually the decision-maker, not the federal government. Further, he says the governor is required to make decisions regardless of who owns a project.

Stratas says short and strict deadlines for litigation will be set. He directed the parties to file their notices of application for judicial review within seven days.

Ecojustice, which brought a case on behalf of Raincoast Conservation Foundation and Living Oceans Society, said it was extremely disappointed with the court's decision and will not rule out taking its fight to the Supreme Court of Canada.

"Going to the country's highest court may seem like a drastic measure, but - in the midst of a climate emergency and biodiversity crisis - these are drastic times," it said.

The Canadian Association of Petroleum Producers said it was disappointed with the court's decision to allow six requests for appeal.

"The (pipeline project) has already undergone a lengthy, thorough and extensive regulatory review process, including extensive consultation with all stakeholders. It has been deemed to be in the best interests of all Canadians."