A US judge has allowed Norwegian Cruise Line to demand that passengers show written proof of coronavirus vaccination before they board a ship, dealing a major blow to Florida Governor Ron DeSantis's effort to ban "vaccine passports."
In a preliminary ruling issued on Sunday, US District Judge Kathleen Williams in Miami said Norwegian would likely prevail on its argument that the "vaccine passport" ban, signed into law by DeSantis in May, jeopardises public health and is an unconstitutional infringement on Norwegian's rights.
The judge blocked DeSantis from enforcing the law against Norwegian, allowing the cruise ship operator to proceed with a plan to resume port activity in Miami on August 15. Violations of the law could have triggered a penalty of $US5000 ($A6800) per passenger, potentially adding up to millions of dollars per cruise.
Raymond Treadwill, a lawyer for DeSantis, did not immediately respond to a request for comment.
The ruling comes as big business and some government entities are responding to the rapid spread of the Delta variant of the coronavirus with vaccination requirements, prompting legal challenges from vaccine skeptics and civil libertarians.
"We are pleased that Judge Williams saw the facts, the law and the science as we did and granted the Company's motion for preliminary injunction allowing us to operate cruises from Florida with 100 per cent vaccinated guests and crew," the company's executive vice president Daniel S. Farkas said in the statement.
Norwegian has said Florida's law would prevent the company from ensuring at least 95 per cent of passengers were vaccinated so it could comply with health regulations when it conducts its first post-pandemic voyage from Miami on Aug. 15.
DeSantis has become a national figure for opposing pandemic restrictions, even as the Republican governor's state has become a hotbed of infections and hospitalisations have hit record levels.
He has argued that Florida law prevents discrimination and protects privacy by preventing businesses, schools or governments from demanding proof of immunity in return for service.
Norwegian has said the law was not about protecting passengers but scoring political points.
Norwegian is ramping up its return to cruises, which the Centers for Disease Control and Prevention (CDC) shut down in March 2020 with its "No Sail" order.
In order to sail, Norwegian has attested to the CDC it would confirm that at least 95 per cent of passengers have been vaccinated.
Norwegian said the law violates the company's First Amendment right to interact with customers and does not prevent discrimination because the company would have to segregate and mask passengers who declined to prove they were vaccinated.
The state argued that Norwegian could have opted, as rival cruise operators did, to seek CDC approval through a process of running simulated voyages and applying other COVID-19 protocols such as masking indoors.