All ferry sailings between Rathlin Island and Ballycastle, County Antrim have been cancelled on Thursday due to industrial action.
The company which runs the service, Rathlin Island Ferry Limited, advised passengers of the disruption on its website.
BBC News NI understands that workers are striking over pay and conditions.
Rathlin Island Ferry Limited operates the service on behalf of the Department for Infrastructure.
A department spokesperson said it “hopes a resolution to the ongoing dispute can be achieved through negotiations between the employers and the union”.
“Emergency cover will remain in place during the strike period,” it said.
BBC News NI has contacted Rathlin Island Ferry Limited and Unite the Union.
Usually, there are 10 sailings per day in January – five in each direction – beginning at 08:00 GMT from Rathlin.
The six-mile journey can take between 25 to 40 minutes.
Rathlin Island is home to a population of about 150 people.
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