Scottish ferry owner CalMac is investigating five seafarers after allegations that they failed breath tests.
Local media said the 659-passenger Isle of Arran (built 1984) was pulled from its route from Islay to the mainland on Tuesday as passengers were waiting to board.
One passenger reported seeing someone taking a breathalyser on to the vessel, the Press and Journal daily reported.
CalMac said: “We can confirm Isle of Arran was taken out of service on Tuesday March 7 due to an HR matter concerning a number of individuals.
"Formal investigations are underway and it is inappropriate to comment further on that matter. We regret that some passengers experienced inconvenience as a result of this.
“As a responsible ferry operator and employer, we take the safety of our passengers, crews and vessels extremely seriously, and will not hold back from doing whatever is required to achieve that.
“All staff, whether on shore or at sea, know what is expected of them and the consequences of failing to meet the high standards of behaviour set by the company.”
The ship returned to a full timetable on Wednesday.
