Seafarers are being offered a consultative ballot on industrial action amid claims seagoing staff at Marine Scotland are being paid thousands less than those on other Scottish government-run contracts.
The Unite union says a chief steward for Marine Scotland can earn up to £29,579 a year, while the same post at CalMac is rewarded with £37,675.
Both Marine Scotland, which manages Scottish waters, including the seas around Shetland, and CalMac are operated by the Holyrood administration.
It comes after the issue was raised before First Minister Nicola Sturgeon by Highlands and Islands Labour MSP, Rhoda Grant.
Unite Scotland’s regional officer, Sandy Smart, said staff faced the threat of losing a “retention allowance” from April.
“We are now going to be running a consultative ballot of members because they feel quite strongly about this matter.
“We will be balloting members to find out if they are prepared to go down the road of a full industrial action ballot.
“That’s going to have an impact in that if there is strike action that takes place there won’t be ships patrolling the sea.”
What form that industrial action will take has not formally be decided. But Mr Smart said feedback from union members was that they were prepared to strike.
“What members are talking about when I met with them last week is they are prepared to take strike action. They are having difficulty in recruiting and retaining staff, which is what the retention payment was for. management have reneged on that and are now denying that that was the case.”
Marine Scotland said it was committed to a pay policy that was “fair for all”.
A spokesman said: “Temporary and supplementary payments are reviewed on a regular basis to ensure staff recruitment and retention, while delivering value for money for Scotland’s taxpayers.
“The Scottish government is currently carrying out a comparative pay analysis of seafarers salaries and, at a meeting in February, Marine Scotland agreed to review any supporting information which the Trade Unions had in support of retaining the pay supplement for a longer period. That commitment remains in place.
“Marine Scotland management is still actively considering the case for the continued payment of a recruitment and retention supplement.”