SOUTH PORTLAND, Maine (AP) — South Portland voters are deciding today whether to adopt an ordinance aimed at preventing the flow of tar sands oil to the city.

Supporters said the proposal would protect the community of 25,000 residents from exposure to harmful toxins, while critics argued it would destroy existing businesses along the city's working waterfront.

Protect South Portland, the group advocating for the ordinance, said the pipeline's owner is hoping to reverse the flow of a 236-mile underground pipeline that transports crude oil from South Portland to Montreal to instead send tar sands oil from Canada.

The proposed ordinance would ban the expansion and enlargement of any existing storage tanks or distribution facilities in some parts of the city.

The pipeline's owner, Portland Pipe Line Corp., has maintained that it has no current plans to reverse the flow of the pipeline, despite floating the idea several years ago. The company recently surrendered the one remaining permit it had from the state in order to prove that such a plan is no longer on the table.

The pipeline company was nevertheless against the proposed ban. Portland Pipe Line and a coalition of other businesses along the waterfront poured hundreds of thousands of dollars into the campaign against it. They said the broadly written ordinance would have the unintended consequences of preventing current petroleum-related and other waterfront businesses from such tasks as regular maintenance.

But Protect South Portland, backed by the Natural Resources Council of Maine and other of the state's environmental groups, insisted that the ordinance would have no impact on existing businesses.