Politicians in Nova Scotia gathered at the provincial legislature Tuesday evening for an emergency debate on the future of the Muskrat Falls hydroelectric project.

The move came just hours after new figures revealed a significant increase in the bottom line over the last two years. It's estimated the project that will dam the Lower Churchill River in Newfoundland and Labrador will cost $7.4 billion.

Nova Scotia Power's parent company, Emera, has agreed to cover 20 per cent of the capital cost. That includes $1.2 billion to build a subsea cable between the two provinces. Emera is waiting for news on a federal loan guarantee that would affect the cost of the subsea cable before it presents a final cost estimate to Nova Scotia's Utility and Review Board.

Premier Darrell Dexter was quick to jump to its defence.

"This is a game changer," he said. "It means the creation of thousands of jobs for Nova Scotians. It means stable energy prices for families, for busineses well into the future. It means a strong economy."

Earlier in the day, Dexter admitted he would not be surprised if the cost of the cable increases as well.

"Well I think it would be understandable over the last couple of years, as labour costs have increased that you'll see some inflation of that figure," he said.

Dexter said Muskrat Falls still has his support as the best way to feed Nova Scotia's power requirements in the years to come.

"The question is what is the lowest cost option for that? And the reality is that this, compared to other alternatives, will be the lowest cost option."

Opposition leaders disagree

The opposition parties are already calling on Dexter to hit the brakes on the project. Both leaders said there's no way to know whether this is the best plan without looking closely at other options including buying electricity from Quebec.

"This premier has signed on to a deal that he doesn't know the cost of," said Stephen McNeil, leader of the Liberal party. "He can't tell Nova Scotians what it will mean to their power bill and at the end of the day, that's what matters."

Progressive Conservative leader Jamie Baillie is also skeptical.

"The premier is rushing through a 50 year decision, a multi–billion dollar project and we don't even know the most basics of how much it's going to cost or what impact it will have on our economy," he said.

In the House, he added to his concerns.

"We have options that Newfoundland doesn't. Hold on. There are a lot of implications to this decision we are going to make."