The Peaks Island ferry glides past the Portland Pipe Line Corporation's terminal facility in South Portland in this 2013 photo where tankers unload oil bound for Montreal.

The fate of a South Portland ordinance that seeks to bar a company from reversing the flow of its 236-mile pipeline to bring oil south from Canada will next head to the Maine Supreme Judicial Court. It’s the latest development in a years-long legal battle over the city’s 2014 policy known as the Clear Skies ordinance.

A three-judge panel of the 1st U.S. Circuit Court in Boston is sending three questions to Maine’s highest court so it can first determine if the ordinance conflicts with state law.

Oral arguments before the Maine Supreme Judicial Court have not been scheduled.

The ordinance prohibits the bulk loading of crude oil onto tankers in the city’s harbor and prevents the Portland Pipe Line Corp. from reversing the flow of its underground pipeline to bring oil south from Canada. The pipeline for years has brought crude oil from South Portland harbor terminals north to Canadian refiners.

Judge John Woodcock in August 2018 ruled the ordinance did not violate the protections of interstate and international commerce in the U.S. Constitution.

The pipeline firm appealed that decision to the appellate court, which heard oral arguments in July. Judges Juan Torruella, Rogeriee Thompson and David Barron said in a decision dated Sept. 23 that it could not rule in the appeal until Maine’s highest court ruled on whether the ordinance violated state statutes.

Under Maine law, the pipeline company’s license, issued by the Maine Department of Environmental Protection, is a legal order that preempts and negates the ordinance, attorneys for the company argued.

They also believe that the ordinance is in conflict with the state’s Coastal Conveyance Act, which gave the Department of Environmental Protection the authority to deal with oil spills and the transfer of oil between vessels and onshore oil facilities.

Two of the questions sent to the state supreme court deal with those issues. The third is a more open ended question about whether any provision of state law preempts the ordinance.

Woodcock last year ruled that the license was not an order and that local ordinances were allowed under the Coastal Conveyance Act.

The questions the appellate court said it needs answered are:

— Is Portland Pipe Line Corp.’s license an “order,” as that term is used in Maine law?

— If the company’s license is an order, is South Portland’s Clear Skies ordinance preempted by Maine’s Coastal Conveyance Act?

— Independent of a specific statute, is there any basis for finding that Maine’s Coastal Conveyance Act preempts South Portland’s Clear Skies ordinance?