The National Energy Board has approved energy giant Enbridge's plan to reverse the flow and increase the capacity of a pipeline that has been running between southern Ontario and Montreal for years.
The green light is subject to certain conditions and requirements.
The decision on the controversial Line 9 comes some four months after the federal regulator held public hearings on the Calgary-based company's proposal.
The board says its decision enables Enbridge to "react to market forces and provide benefits to Canadians,'' while simultaneously implementing the project in a "safe and environmentally sensitive manner.''
Opponents have argued the Line 9 plan — which involves transporting a heavier form of crude — puts communities at risk, threatens water supplies and could endanger vulnerable species in ecologically sensitive areas.
Line 9 originally shuttled oil from Sarnia, Ont., to Montreal, but was reversed in the late 90s in response to market conditions to pump imported crude westward.