SOUTH PORTLAND, Maine (AP) — Maine environmental groups on Saturday called on the federal government to reject proposals to transport tar sands through the U.S. and urged South Portland residents to support an ordinance that blocks the oil from being sent to the city.

The demonstrators gathered on the Casco Bay Bridge between Portland and South Portland to protest what they called the "world's dirtiest and most dangerous form of oil."

"To protect our climate from further disruption and chaos, and to protect pipeline communities like South Portland, tar sands oil needs to stay in the ground in Canada," Glen Brand, director at the Sierra Club's Maine chapter, said in a statement.

The groups want President Barack Obama to deny a permit for the Keystone XL Pipeline, which would carry tar sands from Canada to refineries in Texas.

Protesters are also backing an ordinance on the November ballot in South Portland which has pit environmentalists against businesses along the city's waterfront.

The group behind the ordinance, Protect South Portland, is concerned that a pipeline that currently carries crude oil from Montreal to Portland Harbor would be reversed to send tar sands to South Portland. They say the type of oil carries much more chemicals than crude oil, posing a greater risk to residents' health and the environment.

But opponents say that transporting tar sands is not any more dangerous than other kinds of oil and Portland Pipeline Corp., the company that operates the pipeline, says there is currently no such proposal on the table.

Businesses along the waterfront have also raised concerns that the ordinance — which would ban the enlargement or expansion of any petroleum facilities — is written too broadly and would have a devastating impact on companies.