Staff at six UK airports owned by BAA have voted three to one in favour of striking in a dispute over pay, their union says.
Heathrow, Stansted, Southampton, Glasgow, Edinburgh and Aberdeen airports would have to close if strikes went ahead, BAA said, as key staff such as firefighters were due to take part.
It said the 50% turnout meant the union did not have a clear mandate to act.
Strike dates are expected to be announced next week.
BAA said: "We regret the uncertainty this vote has already caused our passengers and airline customers.
"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."
The Unite union, which says it is fighting a "measly" pay offer worth up to 1.5%, said 74.1% of the 3,054 staff who voted had said yes to strike action. A total of 6,185 staff were balloted.
In addition to the firefighters, the vote was also put to security officers, engineers and workers in various support roles.
Earlier, the much smaller Prospect union, which represents about 100 managerial and technical staff, said its members had also voted in favour of industrial action.
Both sides said they would to try to avert the action through negotiation and the conciliation service Acas said it is ready to facilitate a meeting as soon as one could be arranged.
Unite said it would be meeting on Monday to discuss a strike plan, leaving the weekend open for talks.
It would have to give a minimum of a week's notice, meaning walk-outs could begin from the week starting 23 August.
Some analysts suggest Unite may target the August Bank Holiday weekend that starts on 28 August, but its leaders refused to confirm that.
Tom Hall of the travel guide publisher, Lonely Planet, said travel companies would put in place contingency plans when they knew the strike dates, such as scheduling flying from alternative airports.
"But for Heathrow - one of the world's biggest airports - there wouldn't be the capacity [at other airports]," he warned, meaning some flights would have to be cancelled.
Unite's Brendan Gold said it was not their intention to ruin people's summer holidays.
"The advice we would give to passengers is to put pressure on the company to come to the table to reach a negotiated settlement," he told a news conference.
Prime Minister David Cameron stressed how disruptive any stoppages would be for the UK economy.
"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 said.
Unite is hoping to force BAA to improve its current pay offer.
Staff accepted a pay freeze in 2009, and described the offer for this year - a 1% increase, with the possibility of an extra 0.5% if the union agrees to changes to the company's sickness agreement - as "measly" and "nothing short of confrontational".
The airport operator counters that its offer is reasonable "at a time when BAA and its airline customers are seeing a decline in passengers due to the impacts of recession and volcanic ash".
Unite is also calling for staff to receive a £450 bonus, which had been promised to them if the company had met a certain earnings target.
BAA, which is owned by Spain's Ferrovial, missed the target by 3%. However, Unite said staff deserve financial recognition for coming so close.
The company has also said there will be no additional summer bonus this year, which is usually paid if BAA makes a profit, and is worth about £700.
Unite is currently also in a dispute with British Airways, which has resulted in 22 days of strikes so far this year.
The union has threatened to ballot for further strikes at the airline starting in September.