Civil engineering workers due to strike tomorrow at Heathrow Terminal 5 after unions call improved pay offer "unworkable".
Laing O'Rourke looked to have averted strike action at the start of the week after making an offer of an extra 67p an hour. But shop stewards and workers have complained that conditions attached to the deal are "unworkable" and will now go ahead with tomorrow's action.
National union secretaries held a meeting with Laing O'Rourke officials on Monday, where they agreed to recommend the 67p offer to workers. However, Laing O'Rourke said that for the deal to go ahead a postal ballot would have to be held, and tomorrow's strike called off.
Shop stewards then rejected the offer on the grounds that a postal ballot would be impractical given the number of travelling workers, and to call off the strike at such short notice would be disruptive and unworkable.
The strike is scheduled to last until Tuesday morning.