Southampton airport faces a possible strike by firefighters in a row over pensions.
The Unite union said a ballot for industrial action would open on Friday and the result would be announced on July 13.
It has accused the airport's owners of wanting to replace a final salary pension with an inferior scheme.
Owner AGS Airports said it was committed to finding a solution acceptable to all parties.
The airport said: "Discussions have been ongoing between the company and union representatives regarding changes to the existing final salary (defined benefit) pension scheme since October 2015."
The airport said it had around 30 firefighters among its 180 staff.
Unite regional officer Phil Silkstone told the BBC: "Unite has been in negotiations with AGS over a number of months to come to agreement to significantly reduce the defined benefit (DB) pension scheme costs.
"Then at the point when an agreement was achievable AGS gave 60 days notice to close the DB scheme."
Unite spokesman Shaun Noble said any strike by firefighters could close the airport over the summer months although the prospect of a strike was "a long way off".
The ballot by the Southampton workers follows a decision by the union last week to hold strike ballots over ensign changes at Glasgow and Aberdeen airports, which are also owned by AGS.
The Prospect union, which also represents Southampton airport firefighters, said it planned to hold a similar ballot over pensions changes and would be formally notifying the airport "within the next day or so".
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