SOUTH PORTLAND, Maine — A pipeline company and a water freight organization have filed suit against the city of South Portland, arguing an ordinance effectively banning the shipment of tar sands, or oil sands, from its waterfront violates their constitutional rights.

The ordinance passed last summer in a 6-1 council vote, with industry officials warning they would challenge the “illegal” action.

“Through this ordinance, defendants seek to retard, and in fact have retarded, international and interstate commerce arising out of the trade in crude oil, violating multiple provisions of the U.S. and Maine constitutions as well as state and federal statutes,” Portland Pipeline Corp. and the American Waterways Operators argued in documents filed Friday afternoon in federal court.

Portland Pipeline Corp. owns a pipeline that runs from South Portland to Montreal and is a subsidiary of Montreal Pipeline Ltd. AWO is a national trade association for the U.S. tugboat, towboat and barge industry.

The complaint alleges the ordinance violates the supremacy clause of the U.S. Constitution because “it’s up to federal authorities, not the City of South Portland, to determine how PPLC’s pipelines should be operated, what product they should carry, and whether they should be used for import or export.”

The ordinance also sets a precedent under which individual municipalities may undercut federal decisions regarding international relations, trade and transportation, the plaintiffs argue.

The plaintiffs argue the ordinance violates the commerce clause because it “impermissibly discriminates against and/or excessively burdens” foreign and interstate commerce and intrudes by regulating in areas that fall under federal jurisdiction, they argue.

Additionally, the ordinance interferes and conflicts with federal licenses, eliminates a market for AWO vessels services in transporting such products from the harbor and sets a precedent for inconsistent local

harbor regulation that could cripple import and export activities nationally and invite commerce curtailment from other nations.

The plaintiffs cite several other violations, including due process and inconsistency with the city’s comprehensive plan.

The lawsuit calls on a federal judge to bar the city from enforcing or implementing the ordinance and order the city to cover the plaintiff’s legal costs associated with the suit.

Supporters of the ordinance, which garnered international attention, called it “historic.” The vote came as the Canadian province of Alberta seeks international markets for its oil reserves, which are the third largest in the world after Saudi Arabia and Venezuela. Canada’s National Energy Board in March gave approval to reverse the direction of Enbridge’s Line 9 pipeline from Alberta to Quebec, which could supply the Portland Pipe Line Corp. with tar sands crude to export.

The South Portland vote was the first explicit obstacle the pipeline has faced in reversing its direction to unload tar sands from Alberta at the eastern port. Vermont has stated any pipeline reversal would need to undergo renewed permitting review, but the state has not blocked tar sands outright. Many communities in that state have passed resolutions opposing the transmittal of tar sands within their borders.

The Portland Pipe Line Corp. repeatedly has stated it has no immediate plan to reverse the flow of its pipeline to transport tar sands east, but it has not ruled out the possibility.

The 6-1 vote in South Portland, with Councilor Michael Pock in opposition, makes final an earlier vote and tees up the next stage of the fight that began in a referendum campaign, which sought to prohibit building infrastructure needed to export tar sands from the city’s waterfront. The referendum failed by a narrow margin.

Councilors who opposed the measure in a public letter and at the ballot box in November said Monday they changed their minds after a committee crafted a revised ordinance limited to preventing bulk loading of crude oil onto marine tank vessels.

The lawsuit filed Friday points out the results of the November vote, as well as the city’s failure to explicitly define what “bulk loading” means.

After the council’s vote, at-large Councilor Tom Blake pleaded with pipeline officials not to challenge the ordinance, noting the potential cost of a legal battle. “This ordinance is the will of the people. … All you’re going to do is alienate yourself even further,” he said.

The plea didn’t work.

Attempts to reach city officials for comment Saturday were unsuccessful.

BDN writer Darren Fishell contributed to this report.

Follow Nick McCrea on Twitter at @nmccrea213.