Baggage handlers and other ground staff at Stansted Airport are launching a four-day strike in a row over new rosters.
Members of the GMB and Unite unions employed by contractor Swissport have already taken industrial action, although the company said it failed to have any impact on passengers.
The unions claimed new rosters threaten pay cuts for their members and would mean staff working extra days for free.
Paul Bouch of Unite said: "Sadly, despite the unions' best efforts to resolve this dispute, Swissport is stubbornly sticking to an offer which will see staff work 14 extra days a year for no extra pay - an offer which had already been roundly rejected by our members."
Gary Pearce of the GMB said: "Both unions are committed to settling this dispute. It's a shame that Swissport does not share our commitment to the workforce. Strike action is always a measure of last resort. We hope Swissport sees sense."
The strike will end at 5.30am on Wednesday.