Heathrow Airport staff, including fire fighters and security guards, will launch another strike over new contracts.
Unite members will be stepping down from office on February 5th after four days of industrial action last month.
Heathrow said it has extensive contingency plans and does not anticipate disrupting passenger travel.
The union said different groups of workers will go on strike at different times of the day, affecting firefighters, engineers, campus security, baggage handling, central terminal operations, and land and airside operations.
The union has accused Heathrow Airport Ltd (HAL) of firing and reinstalling workers on substandard contracts.
Unite Officer Wayne King said, “HAL needs to understand that this argument is not going to go away.
“Our members, forced to move home, downsize their lots or give up their cars because of the cuts imposed by Heathrow Airport, are determined to keep fighting.
“Our members worked during the pandemic. Even now, as infection rates continue to rise, they go to work despite putting themselves and their families at risk of infection.
“It is inconceivable that any employer can believe that it is okay to permanently lower the wages of key employees at this point in time.”
A Heathrow spokesperson said: “It is very disappointing that Unite decided to go on strike during the worst of the crisis to hit the aviation sector.
“Our focus was on protecting jobs. So we offered to any frontline colleague who wanted a job at a market salary above the London Living Wage, despite our company losing more than £ 1.5 billion in the past year.
“Since 100% of our colleagues at the front have already accepted the new offer, we don’t consider this strike action to be necessary.
“Nevertheless, we have activated extensive contingency plans that keep the airport open and function safely, as was the case in December.”