The federal government's decision to buy the Trans Mountain pipeline project doesn’t change B.C.'s commitment to protecting its coast, Premier John Horgan said Tuesday.

Responding to the controversial $4.5-billion purchase offer announced by federal Finance Minister Bill Morneau, Horgan vowed to continue with the province's reference case seeking to clarify whether B.C. can control the flow of diluted bitumen from Alberta on environmental grounds.

The fact that the pipeline could soon be a Crown project has no bearing on the case, Horgan argued.

"It doesn’t change the question that we put to the court," Horgan said. "Our reference case remains. I said as much to the prime minister this morning and there was no comment from him on that."

Critics on both sides of the pipeline debate have questioned the federal government's decision, which was announced days before Kinder Morgan's May 31 deadline for reassurance that political opposition wouldn't get in the way of its expansion project.

Morneau described the deal as a "sound investment opportunity," but refused to answer questions about how much more the government will be spending to continue the pipeline construction. The Trans Mountain twinning has been previously estimated at $7.4 billion.

"Rather than go to the court to determine jurisdictions, they're making financial decisions that affect taxpayers and they'll have to be accountable for that," Horgan said.

The premier also encouraged local pipeline opponents to continue making their voices heard, but only "within the rule of law." Hundreds of protesters have already been arrested demonstrating against the pipeline, many for violating a court injunction ordering them to keep their distance from Kinder Morgan's B.C. terminals.

Horgan wouldn't comment on whether the pipeline purchase undermines the federal government's commitment to combatting climate change, but he did suggest it could have a damaging effect on both Alberta and Ottawa's relationships with Indigenous communities.

"Both governments have professed to embrace genuine reconciliation, and I'm not convinced you can necessarily do that when you're disregarding the rights of indigenous groups," Horgan said.

Morneau's announcement has already drawn sharp criticism – and some support – from local First Nations leaders.

The Union of B.C. Indian Chiefs said opponents have no intention of abandoning their opposition to the pipeline, despite the federal government's massive investment.

"We are absolutely shocked and appalled that Canada is willingly investing taxpayers’ money in such a highly controversial fossil fuel expansion project," Grand Chief Stewart Phillip said in a statement.

"No means no – the project does not have the consent it requires, and we will not stand down no matter who buys this ill-fated and exorbitantly priced pipeline."

But Ernie Crey, Chief of the Cheam First Nation and an outspoken supporter of the pipeline, cheered the federal government's purchase offer.

"This is good news for First Nations & all Canadians," Crey said on Twitter.

Reaction among provincial politicians was split as well. Green Leader Andrew Weaver called the purchase a "betrayal," and while Liberal Leader Andrew Wilkinson agreed it was a mistake, he placed the blame squarely on Horgan's shoulders.

"The premier has got to come forward and put the cards on the table, admit his responsibility in this," Wilkinson told reporters. "We have now, in British Columbia, a reckless and erratic government that's showing that investors should have no confidence in this province until the government changes."

On Burnaby Mountain, where protesters have been demonstrating against the project for months, Will George of the Tseil-Waututh Nation said Ottawa's play only strengthens their resolve.

"This changes nothing," said George. "In fact, it just increases the work we have to do."

Protest group Protect the Inlet is also planning a rally to protest the federal Liberals' decision. Opponents are expected to gather outside Science World Tuesday evening.

With files from CTV Vancouver's Ben Miljure and Bhinder Sajan