VANCOUVER -- A lawyer for the federal government says British Columbia is overreaching with an unconstitutional effort to regulate oil and gas shipments through its lands and waters.

The B.C. Court of Appeal is hearing a reference case that asks if the provincial government can create a permitting regime for companies that transport hazardous substances through the province.

Lawyer Jan Brongers says the Canadian government agrees that environmental protection is of critical importance and that there's a need for robust regulatory regimes.

However, he says the proposed amendments to B.C.'s Environmental Management Act must be struck down because Ottawa -- not the provinces -- has sole jurisdiction over interprovincial projects.

Brongers says the proposal is not merely benign environmental legislation, but a "Trojan Horse" that gives B.C. greater power over projects, including the Trans Mountain pipeline expansion.

The province has argued it's not trying to block Trans Mountain or any other resource project, but is aiming to protect against ecological harm and require companies to pay for damages.

First Nations, cities and the environmental group Ecojustice delivered arguments in support of the proposed amendments because they would ensure greater resources for spill prevention and response.

Assembly of First Nations lawyer Julie McGregor called on the court to ensure that its ruling respects and incorporates the rights of Indigenous Peoples to make decisions about their territories.

She says it's time the federal, provincial and territorial governments adopt the United Nations Declaration on the Rights of Indigenous Peoples, which calls for free, prior and informed consent.

"First Nations, as the original guardians of this environment since time immemorial, have always been concerned about the health and well-being of their lands," she says.

"The days where government actions unilaterally infringe upon or extinguish First Nations treaty or Aboriginal rights -- those days are over."

The governments of Alberta and Saskatchewan, as well as Trans Mountain Corp., Enbridge Inc., and the Canadian Association of Petroleum Producers, have filed documents in support of the federal government.