Thousands of Environment Agency workers are to strike for four days later this month in a long-running dispute over pay.
Unison said its members in England will walk out from 7pm on April 14 until 7am on April 17, adding that communities, waters and wildlife will be put at risk.
Unison accused the Government of making no attempt to hold talks to resolve the row, despite months of strikes and other forms of industrial action.
The latest strike will involve union members who work on coastal sea defences, protect communities from floods, tackle water pollution, waste fires and fly-tipping.
Unison said “endemic” low pay means the Environment Agency (EA) is struggling to hold on to experienced staff and recruit new employees.
Unison said the Government’s refusal to allow the Agency to improve a pay increase of 2% plus £345 given to staff in the autumn means workers have no alternative but to “reluctantly“ strike again.
Emergency “life and limb cover” has been agreed where there is a threat to life or property.
Unison’s head of environment, Donna Rowe-Merriman, said: “Every community in England needs these experienced employees to help keep their local environment safe.
“All talk and very little action best describe the Government’s approach to environmental policy. Announcements come and go, but nothing much happens to clean up England’s seas, rivers, lakes, and canals.
“This must change. The Government needs a properly staffed Environment Agency if natural habitats and water sources are to be protected. But with too few experts on its books, the Agency can’t possibly punish the polluters and keep everyone safe.
“Therese Coffey (Environment Secretary) should stop ignoring the plight of these invaluable workers and start tackling the growing staffing problems at the Environment Agency.
“Hourly rates are so low, some staff had to be given an emergency pay rise at the start of the week or their employer would have been in breach of minimum wage laws.
“It’s time the Government called in the employer and the unions to settle this damaging dispute once and for all.”
An Environment Agency spokesman said: “As a public sector organisation the Environment Agency remains bound by the pay policy of the government of the day.
“We have plans in place to minimise disruption to our essential work to protect the environment and respond to critical incidents.”