The firm's 928-strong civils workforce rejected a 22p an hour offer last week and voting papers over three planned days of industrial action were sent out yesterday (Wednesday).
But the contractor is holding firm in the hope that support for a strike will crumble in the run-up to Christmas.
A Laing O'Rourke source said: 'We are still open to negotiation but remain convinced that these demands are unjustified and won't be met.
'The T5 lads are the best paid in the industry - you only have to look at what it would cost them to go on strike.
A grade two general operative would lose £472 in wages by striking for three days while a craftsmen would lose out by £658.
'The whole system seems unfair. We employ 928 operatives but only 530 are in the union. That means if only 266 voted to strike then the whole lot would have to come out, which seems plain daft.'
Union leaders are looking for a ballot result by the start of next month with action planned around Christmas.
TGWU regional organiser Alan Brkljac said: 'The bonus payments have not been reviewed for three years. £1 an hour, which means less than £50 a week, is a fair demand to a very profitable construction company working for a client whose profits have increased monthly on the back of rising passenger numbers. 22p an hour is simply not acceptable.'
A BAA spokeswoman said: 'We are disappointed the trade unions have decided to ballot their members as we believe the offer made by Laing O'Rourke is reasonable. We await the result of the proposed ballot and will manage any potential impacts.'
The O'Rourke source said: 'BAA has just tried to do everything in an industry-leading way and now this happens. I feel sorry for them.'