Heathrow is bracing for nearly a month of strike action starting next month.
Unite union members are planning 41 strikes over a 23-day period starting 2 April.
The union said it was taking action after accusing Heathrow of cutting pay and reducing conditions by "firing and rehiring" its entire workforce.
Heathrow has denied the claim, stressing frontline workers have accepted new pay offers paying "above market rate and London living wage".
Airport staff across engineering, airside and landside operations, fire service, security and central terminal operations will walk out during the strike period.
Each sector, said Unite, would take seven days of strike action, meaning at least one sector will be on strike most days during the proposed action.
Unite said some Heathrow workers had experienced pay cuts of up to £8,000, and has claimed that if Heathrow was seeking to cut costs owing to the impact of Covid-19, any pay reductions should have been temporary.
Workers took a ninth day of strike action last week (12 March), with Unite accusing Heathrow of failing to come to the table, resulting in the proposed strikes lasting longer than it had initially intended.