Thousands of fliers face travel chaos after workers at British Airport Authority (BAA) airports -- including Heathrow -- voted overwhelmingly to strike in a fight over pay.
A ballot over pay involving 6,000 staff resulted in a three-to-one vote in favor of strike action, the Unite union said.
Unite will meet with its key representatives on Monday to decide what form of industrial action its members will take.
No walkout dates have yet been announced.
Action will not only affect Heathrow but also Stansted, Southampton, Glasgow, Aberdeen and Edinburgh airports.
On average more than 300,000 passengers a day travel through the six airports.
Unite national officer Brendan Gold said: "This ballot reflects what our members feel about BAA's current attitude."
A BAA spokesman said the company regretted "the uncertainty" that the vote has caused passengers and airline customers.
"We hope that the union will engage with us quickly to conclude an agreement," he said. "Fewer than half of those people eligible to vote have done so and we do not believe this result provides a clear mandate for strike action."
Earlier, Prime Minister David Cameron had said any strike would be futile.
"These sorts of strikes never achieve anything apart from damage -- damage to business, damage to jobs, damage to the interests of tourists who want to come to visit Britain, or people who want to leave Britain and have a holiday overseas," he told reporters.
Unite had urged firefighters, engineers and support and security staff at BAA airports to vote for industrial action over what it called the Spanish-owned company's "measly" pay offer.
The union said staff had already accepted a pay freeze in 2009 and that this year the company had offered staff a 1 percent rise, plus 0.5 percent, which was conditional on changes to a sickness agreement.
Unite also wants workers to receive a performance-related bonus which it said was promised to them if the company hit a certain financial target.
Sky's Scotland correspondent James Matthews, at Edinburgh airport, said the mood among the public and management staff was one of "dismay."
He added: "If it's not companies going bust then it's volcanic ash, and if it's not that then it's BA staff on strike."