Workers on the terminal five building site at Heathrow are staging a three-day walkout in their continuing row over pay.
Scaffolders, labourers and others went on strike today after a new offer to increase bonus pay by 80p an hour was rejected.
The workers are demanding a £1-an-hour rise in bonuses and have already taken part in strikes in December and earlier this month.
Employers Laing O’Rourke had previously offered an extra 67p per hour.
Phil Davies, of the GMB union, said: “Laing O’Rourke have misjudged the mood of the workforce right from the start of this dispute.”
Heathrow Airport maintains that industrial action has not disrupted building work.