The cruise ship Adventure of the Seas sits off Bar Harbor on Mount Desert Island on June 4, 2018. Gregory Rec/Portland Press Herald

Bar Harbor’s 1,000-person daily cap on cruise ship visitors got unusual scrutiny Wednesday when retired U.S. Supreme Court Justice Stephen Breyer joined the panel of judges reviewing the case at the 1st Circuit Court of Appeals in Boston.

Breyer and two other judges heard the appeal of last year’s U.S. District Court decision in Bangor that upheld the cap.

Lawyers defending the town’s ordinance called Breyer’s appearance an “unexpected delight” and described the cap as necessary to maintain public safety amid rising cruise ship visits.

It was proposed in response to complaints about downtown congestion during the cruise season, when more than 150 ships typically visit, some carrying several thousand passengers.

Lawyers for businesses challenging the cap disputed that cruise ship visitors pose a public safety threat that warrants blocking 80% to 90% of passengers from disembarking.

Bar Harbor voters approved an ordinance in November 2022 that limits the total number of cruise passengers that can disembark from any cruise ships to 1,000 per day.

A previous cap limited cruise ship visitors to 65,000 per month under an agreement with the cruise lines. Last fall, town voters narrowly rejected a proposal from the town council that would have raised the daily cap to 3,200 passengers.

A group of businesses sued the town, claiming that the 1,000-visitor cap is unconstitutional because it violates clauses ensuring the supremacy of federal law and protecting interstate commerce. The group includes the Penobscot Bay and River Pilot Association and the Association to Preserve and Protect Local Livelihoods.

Judge Lance Walker in the Bangor federal court found in favor of the town last February, deciding that Bar Harbor had home rule authority granted by the state.

On Wednesday, the three appellate judges lobbed questions at attorneys on both sides in an effort to clarify issues of the case before handing down a ruling at a later date.

The judges questioned whether limiting cruise passengers was any different from setting a limit on visitors to a municipal, state or national park.

The judges also questioned whether the cap violates interstate transportation and commerce laws by limiting cruise ship passengers, but not visitors who travel to Bar Harbor by car, bus or bicycle.

Jonathan Benner, an attorney for the businesses, said his clients are concerned that Bar Harbor’s cap could “metastasize” and be adopted by other communities that want to limit or block certain people altogether.

Jonathan Hunter, an attorney defending the ordinance, said it is an expression of the town’s home rule authority to manage “acute congestion” that clogs its quaint streets, shops and restaurants during the cruise ship season.

Hunter compared the cap to South Portland’s Clear Skies Ordinance, which blocked the Portland Pipe Line Corp. from reversing the flow of its pipeline to bring crude oil from Canada. The city ultimately prevailed in 2021, when the company dropped its six-year fight in federal court.

The judges questioned Hunter’s use of the word “crush” to describe congestion created by cruise visitors, whose numbers can double the town’s population of 5,500 for an afternoon.

They also noted that Bar Harbor’s effort to maintain the town’s tranquility and quality of life impacts residents of communities far beyond Maine whose ability to visit is curtailed or blocked.

Breyer, 86, was invited to return to the 1st Circuit bench and “happily agreed,” the Associated Press reported.

Breyer served 14 years with the 1st Circuit, appointed by President Jimmy Carter in 1980. President Bill Clinton appointed him to the Supreme Court in 1994 and he retired in 2022.

The 1st Circuit hears federal appeals from Maine, Massachusetts, New Hampshire, Puerto Rico and Rhode Island.