Saudia is among the airlines that could feel the effects of the strike by workers at Red Handling.
Unite said about 230 workers, including passenger assistance staff and ground handlers, will strike in tranches between August 18 and 28.
Red Handling is also responsible for ground handling operations for Norse Atlantic, Norwegian, Delta, and TAP Air Portugal at Gatwick.
The union claims Red Handling and another company, Wilson James, have “failed to make offers that meet the workers' expectations”.
“Red Handling and Wilson James need to wake up and smell the coffee,” said Unite general secretary Sharon Graham.
“Other employers at the airport are prepared to pay the going rate and there is no excuse why they shouldn't do the same. There is no way our members will accept a real-terms pay cut and poverty pay.
“Unite's complete focus on the jobs, pay and conditions of its members will mean that our members at Gatwick will receive the union's unflinching support.”
Unite members working for Red Handling will walk out for four days from August 18, and a further four days from August 25, which includes the August bank holiday weekend.
Members of the union employed by Wilson James, which operates Gatwick's passenger assistance contract, will walk out for three days from August 18, and a further three days from August 22.
Unite believes 216 flights could be disrupted during the first four-day strike, which it claims will affect around 45,000 passengers.
Ground handlers employed by four other companies at Gatwick – ASC, Menzies Aviation, GGS and DHL Services – cancelled strike action after receiving improved pay offers.
Ms Graham praised the “excellent” deals and credited the results to unionised workers standing strong during talks.
Those workers had planned to strike on two successive weekends starting July 28 and August 4.
Cancellations and delays at Gatwick left thousands of passengers stranded in late July.
Up to 11,000 people were affected due to adverse weather and staff shortages, resulting in the cancellation of more than 70 flights.
Unexpected thunderstorms across Europe coupled with air-traffic control staff shortages led to one-tenth of flights being cancelled within 24 hours.