Another strike by workers building a £4bn fifth terminal at Heathrow Airport is to begin on Friday.
Scaffolders, labourers and other workers have already held a two-day walk out in a row over bonus pay.
The GMB union expects hundreds to join the action on Friday and Monday, and has banned weekend overtime.
A Heathrow spokeswoman said 850 of an 8,000-strong workforce are expected to take part, stressing no delay would be caused to the T5 programme.
Workers want an extra £1 an hour in their bonus schemes but contractors Laing O’Rourke are offering 22p.