The resolution passed by a vote of 7-2 in a late-night session held in Portland's council chambers.
"The most important part is that we send a message to state leaders and national leaders that [this] is something we really need to look into and do our due diligence on," said Coun. David Marshall, the chair of the city's transportation, sustainability and energy committee that drafted the resolution.
Earlier this year, Portland council sent another oilsands-related resolution back to committee without voting on it.
Monday's resolution is one in a string of similar resolutions passed in towns across Maine. It is part of a campaign spearheaded by Environment Maine to stop Alberta bitumen making its way through the Maine countryside.
"We're really pleased the Portland City Council passed a resolution to protect our drinking water," said Environment Maine director Emily Figdor. She explained that the Portland Montreal pipeline runs right next to some of the state's most important drinking water sources, including Sebago Lake.
The dual pipeline was built during the Second World War to transport oil from Portland to Montreal for refining. Now one of the pipes is empty and the company is open reversing the flow for the first time to ship Canadian oil to the U.S.
The problem for activists, said Figdor, is that because the pipeline is already in the ground neither a presidential permit nor an environmental assessment needs to be done to change directions on the pipeline.
"What it comes down to for me is that diluted bitumen behaves differently in water than regular crude," explained Marshall. He said diluted bitumen separates when it enters water. The diluting agent or lubricant evaporates and the bitumen sinks to the bottom making it very hard to clean up. Marshall pointed to a 2010 spill in the Kalamazoo River in Michigan as an example.
"That's really the red flag for me," he said.
CBC contacted the Portland Montreal Pipe Line company for comment but received no reply.Suggest a correction