The plan to convert the coal-fired power generation plant in Thunder Bay, Ont., to natural gas has hit a major roadblock and may not happen at all.

On Wednesday, the province cancelled the planned construction of a gas line that's essential to the northern Ontario project. The government said the decision is temporary while the need for the $400-million conversion project is reviewed.

The Ontario Power Authority said options like a new transmission link near Wawa, Ont., to the rest of the provincial grid could ensure the northwest region's electrical needs are met without rebuilding the Thunder Bay station.

The Northwestern Ontario Municipal Association is angry the province has put the brakes on the Thunder Bay project. It says the news comes despite assurances from the government as recent as August that the project would proceed.

"These actions jeopardize the conversion and also put at risk billions of dollars of investment in the mining sector by raising concerns that the required power may not be there when it is needed," NOMA president Ron Nelson said.

"Why is (the Ontario Power Authority) determined to turn off the lights in our region?"

The province has ordered all of Ontario's power generating stations to end the use of coal by 2014. Thunder Bay's station, along with the one in Atikokan, have been operating at minimal levels since 2008.

Atikokan burned its last load of coal in September and is now shut down completely as it gets converted to use biomass as a fuel at a cost of $170 million. It's scheduled to be operational again in 2014.