Coastguards and other Maritime and Coastguard Agency (MCA) workers are to vote on industrial action in a dispute over a below-inflation pay offer.
There are about 400 MCA search and rescue teams covering the UK
Some 700 Public and Commercial Services union members will be balloted on taking action short of a strike.
General secretary Mark Serwotka said the basic coastguard grade was paid barely above the minimum wage.
Meanwhile, over 20 volunteer coastguard teams are still refusing to go on call-outs in a row over injury cover.
In the PCS dispute the union said many workers would receive a below-inflation increase of 2.5% while the most experienced staff would get less than 1%.
Negotiating officer Paul Smith said members were angry about the unwillingness of management to negotiate.
He also claimed they had disregarded a pay comparison study with other 999 services - which had "fuelled members' sense of betrayal".
Mr Serwotka said members monitored shipping and public safety across tens of thousands of square miles of ocean and coastline but many earned £5.37 an hour for a 42-hour week.
"You have to ask yourself - is it right that people providing such an essential service are being asked to take a real terms pay cut?" he said.
The dispute involving volunteer rescuers, which started on Tuesday, revolves around the case of a Pembrokeshire volunteer who was seriously injured while rescuing an animal from a cliff face four years ago.
He subsequently lost his job as a residential social worker.
Colleagues from other teams went on "strike" in support of his case, claiming he had not been adequately compensated.
But managers at the MCA - who met one of the teams on Thursday evening - said earlier the volunteers were "acting on misinformation"
Anthony Rogers, a member of the Fishguard team, said colleague Brian MacFarlane had been classed as partially disabled since the cliff accident.
But Mark Clark, spokesman for the MCA, said it had paid Mr MacFarlane substantial amounts, non-taxed, in order to cover him.
"Payments also continue to be made to Mr MacFarlane from the Civil Service Injuries Scheme and the total package compensates him for loss of his previous full-time work."
He said he could not divulge the amounts Mr Macfarlane had received.
His colleagues claimed he was receiving a temporary payment of less than half his old salary.
Mr Clark said they had offered to set up a working group with the Fishguard team and to make representations to the civil service scheme.
"We don't want them to put themselves at risk and be heroes, but to get on with the job and rescue fellow citizens where they can. If by chance they are injured they will be compensated until they get better and can return to work.
"There is no secret about the fact we are concerned about coastguards withdrawing services, but we feel they are doing so on misinformation," he said.
The five-and-a-half hour meeting between Fishguard volunteers and the MCA on Thursday ended without resolution - but both sides said progress had been made.