Specialist baggage handlers a Heathrow plan 24 days of strike action in March.
The workers employed by Global Baggage Solutions at the airport are responsible for finding and repatriating lost baggage with distraught passengers.
The dispute over pay follows two walkouts in February by members of the Unite union.
The fresh strike action is planned for March 2-9, 14-21 and March 26-April 2.
Unite regional officer Clare Keogh said: “Passengers using Heathrow in March need to be aware that if their luggage disappears it is likely to be trapped in a black hole
“The strikes also expose that Heathrow is far from a living wage employer, as in order to achieve this all of the airports sub-contractors and supply chain must abide by the rules.
“Further strikes can still be avoided but Global Baggage Solutions must be prepared to put more money on the table.
Travel Weekly has tried to contact Global Baggage Solutions for a response.