OTTAWA -- The country's highest court has ruled that the federal government can rely on the National Energy Board to fulfil its duty to consult Indigenous communities about development projects in their traditional territories -- but only if the process is robust.

In unanimous decisions in two separate appeal cases which were heard together because of their similar issues, the court found the NEB did indeed fulfil the duty properly in one case -- the reversal of the Line 9 pipeline in southwestern Ontario.

But the court said the regulator did not fulfil its duty in the other case -- seismic testing near Clyde River in Nunavut.

The cases go to the heart of how Indigenous consultation has to take place when resource development projects are proposed on their territories.

The court sent a sharply worded message to the government and the NEB that proper consultation ahead of time is always better than asking the courts to undo it later.

In the case involving the Inuit Hamlet of Clyde River in Nunavut, the court found the NEB failed miserably at fulfilling the duty to consult the Inuit regarding proposed seismic testing in and near marine areas where they have treaty rights.

In the other case however, the court found the NEB did properly consult the Chippewas of the Thames First Nation about an Enbridge pipeline project expansion in its territory by specifically considering the impact on treaty rights and ensuring adequate access and assistance to participate in the hearings.

The key difference in the two cases was largely that when it came to the Chippewas, the regulator's review specifically assessed the impact on treaty rights as is required.

In the Inuit case, the NEB looked at environmental impacts without directly considering whether the proposed testing would affect treaty and indigenous rights.

The proposed seismic testing was to take place over five years, and involve shooting air guns through the water to look for oil reserves.

The waters were populated by marine mammals such as whales and seals and polar bears which the Inuit rely on for their livelihood, food and cultural practices.

The NEB's environmental assessment did find the testing could increase the mortality risk to the mammals, cause permanent hearing damage and affect their migration routes. That finding, the court held, meant the Crown's duty to consult was "at the highest end of the spectrum."

Yet the consultation "fell short in several respects" the court found.

That included the fact the proponents couldn't initially answer Inuit questions about the impact on the mammals, and when they did answer them months later, the answers were delivered in a nearly 4,000 page digital document the Inuit couldn't download because of the poor Internet speeds in the far north.

"To put it mildly, furnishing answers to questions that went to the heart of the treaty rights at stake in the form of a practically inaccessible document dump months after the questions were initially asked in person is not true consultation," wrote the court.

The court also issued a stern warning that the consultation process on Indigenous rights has to occur before projects are approved.

"True reconciliation is rarely, if ever, achieved in courtrooms," the judgement says. "Judicial remedies may seek to undo past infringements of Aboriginal and treaty rights but adequate Crown consultation before project approval is always preferable to after-the-fact judicial remonstration following an adversarial process.

"No one benefits -- not project proponents, not Indigenous peoples, and not non-Indigenous members of affected communities -- when projects are prematurely approved only to be subjected to litigation."

The ruling means seismic testing near Clyde River cannot go ahead.