AMEC civil engineering workers at Heathrow's T5 held pay talks with management this week to demand terms on a par with the deal struck with Laing O'Rourke staff last week.
Trade union representatives met Amec on Tuesday to put in a claim for an extra 80p an hour and £800 back pay ? a settlement that was agreed by 900 Laing O'Rourke workers.
Amec has around 350 employees on the site who will be seeking the extra cash.
A union source said: 'We are in negotiations at the moment but the main thing that we want is parity. What is good enough for Laing O'Rourke men is good enough for Amec men and we will make it clear that anything short of that will lead to industrial action.'
Construction union Ucatt, T&G and the GMB were originally pushing for an extra £1 an hour to match the deal struck by electricians on the £4.2 billion project last year but accepted the 80p offer after seven days of strike action.