A decision by Canada's National Energy Board on Thursday brings oil extracted from tar sands a step closer to New England, alarming a coalition of Vermont environmentalists.

The board authorized the Canadian energy company Enbridge to reverse the flow of crude oil in a section of its Line 9B pipeline running from Westover, Ontario, to Montreal.

Vermont environmentalists immediately expressed concern that the decision could lead to the reversal of flow in a pipeline that traverses northeastern Vermont. The 263-mile Portland-Montreal pipeline currently carries light crude oil from Maine through the Northeast Kingdom to Quebec. Owner Portland Pipe Line Inc. has not applied for a reversal of flow, but activists fear the company may seek to allow crude to flow from Montreal to Portland.

An Enbridge spokesman said Thursday the company has "no interest" in using the Portland-Montreal pipeline to move tar sands oil.

If the Portland flow was to be reversed, Thursday's decision would create the logistical opportunity to move crude from Western Canada's tar sands fields to a seaport from which it could be shipped to refineries. That could provide Enbridge with an alternative to building the controversial Keystone XL pipeline through the Central Plains states.

Environmentalists are concerned that the heavier, tar sands oil might lead to leaks in the 63-year-old Portland-Montreal pipeline.

More than a dozen Vermont communities voted on Town Meeting Day to oppose the reversal of flow.

Enbridge said 300,000 barrels a day will move east to two Quebec refineries through the 30-inch Line 9B pipeline, up from 240,000 barrels a day that were transported in the opposite direction.

Graham White, a spokesman for Enbridge, said that amount is less than the two refineries it seeks to serve can process, meaning there is no surplus oil to send further east.

"The combined capacity (of the refineries) is 400,000 barrels," White said. "It makes no mathematical sense."