Sea rescue dispute.
They will stage a 48- hour stoppage over the bank holiday in a long-running row over wages.
The Public and Commercial Services Union (PCS) said its members were angry at being paid less than the other emergency services.
Mark Serwotka, PCS general secretary, urged the public not to take to the sea unless it was essential to do so.
As many as 700 Maritime and Coastguard Agency staff are expected to take part in the stoppage nationally, which will begin at 7pm tomorrow and end at 7pm on Monday. The MCA said contingency plans were in place to ensure an emergency service was available during the strike.