Members of the Fire Brigades Union (FBU) are campaigning against plans to cut about 180 firefighters and control room jobs in the county.
The union said it would lead to a 20% reduction in full-time uniformed staff.
The fire authority said "strong resilience arrangements" were in place to cover the strike period.
FBU official Keith Handscomb said Essex Fire and Rescue Authority was "putting people's lives at risk" with the cuts.
"They will trot out statistics, but the fact is more than three people are rescued from emergencies by Essex firefighters every day," Mr Handscomb said.
"That is three people every day in Essex who cannot afford any cuts in frontline fire and rescue services."
The union said it had planned to strike for short periods but had effectively been "locked" out until Friday evening.
In a statement, the authority said: "In the interests of public safety, Essex Fire Authority has decided that on this occasion, it will not accept partial performance and therefore will put its well-rehearsed resilience arrangements in place to cover the entire strike period.
"This means that firefighters withdrawing their labour for any part of a shift will not be required, or paid, for the whole shift.
"The service will have greater availability with its resilience arrangements in place than it would under the complicated arrangements set out by the FBU for strike action among various work groups at different times over the three-day period."
The union is involved in an ongoing dispute with the government over pensions.
Firefighters in Essex have started a three-day strike in a row over jobs, warning that planned cuts would put lives at risk.