Office-based coastguards across Britain and Northern Ireland will start a 48-hour strike today over a long-running pay dispute.
As many as 700 Maritime and Coastguard Agency (MCA) staff could take part in the action, which will begin tonight and end on Monday.
The Public and Commercial Services Union (PCS) said its members are angry at being paid less than the other emergency services.
The PCS held five days of strike action earlier in the year, leading to the closure of nearly half of the UK's rescue co-ordination centres. The PCS urged the public not to take to the sea unless it was essential to do so.
The MCA has said contingency plans were in place to ensure an emergency service was available during the strike, but urged the public to take extra care while on the sea, beach or cliffs.
The MCA said the industrial action was being taken by people responsible for co-ordinating rescues, and the rescuers themselves would operate as normal.
Rescue helicopters will continue to fly, Royal National Lifeboat Institute (RNLI) boats will go out and volunteer coastguard rescue officers will be ready, the agency said.
PA