Coastguards will start a 48-hour strike over a long-running pay dispute.
As many as 700 Maritime and Coastguard Agency (MCA) staff could take part in the action, which will end at 7pm on Monday.
The Public and Commercial Services Union (PCS) said its members are angry at being paid less than the other emergency services.
The August Bank Holiday stoppage follows five days of strike action earlier in the year, which the PCS said led to the closure of nearly half of the UK's rescue co-ordination centres.
Mark Serwotka, the PCS general secretary, said he expected this weekend's stoppage to be as well-supported as previous strikes, and urged the public not to take to the sea unless it was essential to do so.
"Strike action is a last resort for our members who provide an invaluable service in ensuring the safety of shipping in British waters," he said.
"The latest action could have been avoided if the Government and the Maritime and Coastguard Agency (MCA) hadn't continued with their refusal to negotiate a satisfactory outcome.
"Members have rightly grown angry at the scandalous refusal to pay them the same as other emergency service workers, and by the government's policy to cap public sector pay increases below inflation."
The union said staff have experienced real-terms pay cuts with pay rises averaging just 2.5% for most staff, and less than 1% for senior personnel.
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.
