The trade union Unite is warning Birmingham airport management that they are forcing a dispute with workers over a pay offer after a three year pay freeze.
The union say they are now preparing for an industrial action ballot.
Birmingham Airport's bosses are offering a 2.5% increase in pay and a one-off non-consolidated payment of £150.
Workers have previously seen changes to their terms and conditions, their pension scheme and now changes to the shift patterns are proposed.
Last year, the airport made profits, after tax, of £5.2 million. They are looking to extend the runway to allow long haul flights from Australia and America to land, increase passenger numbers and open new routes.
The airport's pay offer has been rejected at two separate members ballots, with the most recent returning a rejection vote of 76.5%.