SOUTH PORTLAND  (AP) — A proposed ordinance designed to block tar sands oil from being transported to South Portland has set off a fiery debate over what impact it will have on the community and the city’s bustling waterfront.

Opponents of the thick, gooey oil derived from tar sands in Canada fear a 236-mile underground pipeline that transports crude oil from South Portland to Montreal could be used in reverse to send tar sands oil from Canada through Maine.

They say the proposed ordinance, which will appear on the Nov. 5 ballot, is the only way to ensure the oil doesn’t flow into the city, harming the environment and residents’ health. Their concerns mirror those against Canada’s Keystone XL pipeline that would carry tar sands oil to the Gulf of Mexico.

But critics of the local proposal say it is too broadly written and its passage will stifle future development of existing tank farms, distribution centers and other petroleum facilities that line South Portland’s waterfront.

“You’re taking a potential impact of hundreds, if not thousands, of jobs and millions of dollars in investment in the community,” said Chris Bowring, former South Portland mayor and city councilor, who has joined opposition to the proposed ordinance.

South Portland’s oil terminals are some of the largest on the East Coast; the port brings in millions of barrels of refined products, such as heating oil and diesel fuels.

Protect South Portland, the group behind the proposal, says Portland Pipe Line Corporation hopes to use the pipeline to transport tar sands oil and build nearby smoke stacks. While the company made that proposal in 2008, it says no such project is in the works now.

The anti-tar sands group, which gathered more than 3,000 signatures to get the ordinance on the ballot in the community of 25,000 residents, says the oil is dirtier than most other heavy crudes refined in the United States and riskier to transport. It also contains harmful chemicals and releases greenhouse gases that contribute to climate change, the group says.

“The long-term effects cause cancer, create lung disease … It would totally change our way of life,” said Cathy Chapman of Protect South Portland, which has the support of Mayor Tom Blake.

She sees the oil company’s fierce opposition to the proposal as evidence that it has its eye on transporting tar sands.

Several Maine communities have passed symbolic resolutions opposing the oil, but Protect South Portland says the only way to make sure no tar sands plan moves forward is by passing the ordinance.

The city can’t regulate pipelines, and the proposed ordinance doesn’t mention tar sands. Instead, it seeks to ban the expansion and enlargement of any existing petroleum storage tanks or distribution facilities in South Portland’s shipyard district and other areas, a move that would be necessary to reverse the pipeline and pump tar sands into the city.

But opponents say that language would also prevent existing petroleum-based companies from doing routine maintenance and upgrades and would eventually cause them to shut down.

“What they don’t say is that it’s also going to put a lot of other businesses out of business,” said Jim Merrill, spokesman for Portland Pipe Line. “I think a lot of people out there signed this (petition) thinking it was one thing and are now waking up to the realization that this is something far different.”

Natalie West, a former lawyer who helped craft the anti-tar sands ordinance, said the proposal is narrowly crafted to ensure that it blocks tar sands oil without having any significant impact on existing businesses.

“There’s nothing in the language of the ordinance that will hurt business as it exists now,” said Carol Masterson, a member of Protect South Portland.

Efforts by both sides to convince voters are now in full swing.

Anti-tar sands organizers have rented an office space to serve as headquarters and are putting up signs and knocking on doors to get votes. Chapman says their group is relying almost entirely on donations and volunteer hours from environmental groups, like the Natural Resources Council of Maine.

Meanwhile, opponents of the ordinance have hired several media consultants and lawyers. They are garnering support from businesses along the waterfront and running advertisements, and they recently produced a report on the detrimental economic impact the ordinance could have, including the loss of 5,600 jobs and $250 million less in annual earnings over the next 10 years.