Firefighters in Essex struck for three hours on Saturday night last week. The FBU members are fighting job cuts in the county.
The union says bosses are building up their cash reserves while cutting firefighters and equipment. Bosses have also stepped up disciplinary measures against the workers.
The dispute has so far seen three years of action short of a strike, a series of short strikes, and a one-day strike last month.
A strike previously planned for this Saturday was called off. The firefighters plan to strike again for four hours on 5 September.