British Airways cabin crew have voted overwhelmingly in favour of strikes in a row over pay.
Unite said its members backed walkouts by 4-1, raising the threat of disruption to flights.
The dispute involves cabin crew who have joined the airline since 2010, with Unite claiming they earn less than other staff.
Turnout in the ballot was 60%.
Unite said around 2,500 workers in BA's so-called Mixed Fleet are involved in the dispute.
The union claimed earnings were advertised between £21,000 and £25,000 but in reality started at just over £12,000 plus £3 an hour flying pay.
Unite regional officer Matt Smith said: "Our members have overwhelmingly voted for strike action because British Airways' pay rates are indefensible and the crew are at breaking point.
"Mixed Fleet crew earn just over the minimum wage and below the national average. Significant numbers of crew are taking on second jobs, many go to work unfit to fly because they can't afford to be sick. British Airways bosses need to wake up to the anger and the injustice here.
"Not only are the pay rates indefensible but, in aviation, low pay is a safety issue. Thirty percent of the Mixed Fleet crew have been with the company for just under a year.
"Crew simply can't afford to stay. Inexperience, fatigue, and the fact that BA recently cut the length of crew training courses means Unite is genuinely concerned about the potential repercussions.
"We urge British Airways to avoid this dispute and do the right thing by both the frontline staff and the travelling public, by engaging with Unite to negotiate a genuinely meaningful way forward."
A BA spokesman said: "We are extremely disappointed that the union is creating uncertainty for our customers.
"Mixed Fleet Unite represents about 15% of our cabin crew. We remain focused on resolving this issue as quickly as possible without any disruption to customers.
"We have proposed a fair and reasonable pay increase to Mixed Fleet cabin crew which is in line with that accepted by other British Airways colleagues and which will ensure their reward levels remain in line with cabin crew at our airline competitors."