British Airways (BA) has begun cancelling hundreds of flights ahead of another pilots’ strike on September 27.
Tens of thousands of passengers are expected to be affected by the disruption.
The 24-hour walkout follows a two-day strike on Monday and Tuesday when 1,700 flights were cancelled, affecting over 195,000 passengers.
The airline started contacting affected passengers on Thursday afternoon, 15 days ahead of the strike.
Under EU law, passengers are only entitled to compensation if they receive less than 14 days’ notice of a cancellation.
The strikes began over pay disputes between members of the British Airline Pilots’ Association (Balpa) and the airline.
BA has offered a pay rise of 11.5% over three years, which it says would boost the pay of some captains to £200,000, but Balpa says its members want a bigger share of the company’s profits.
Both sides have said they want to resume talks, but there is little sign of the deadlock being broken, as they continue to point the finger at each other.
A spokeswoman for BA said: “On August 23, Balpa, the pilots’ union, called a strike on September 27. It is now a month since we shook hands on a pay deal. We urge them to call off their strike and return to negotiations.
“To give our customers as much certainty as possible, we are now contacting all those affected to offer them a full refund or a re-book on an alternative date, destination or airline.
“We are very sorry that Balpa’s actions will affect thousands more travel plans.”
In response, Balpa has slammed BA for being "irresponsible and inconsiderate", tweeting: "We understand that BA has started cancelling its operations on the 27th of September today outside of the 14 day window to avoid having to compensate affected passengers.
"BALPA set a gap between the first and second periods of strike action to give BA time to work with us to settle this dispute with their pilots.
"We had today been exchanging new ideas to do that via ACAS and so it irresponsible and inconsiderate to its customers that BA has pulled out and decided to start canceling flights now, just to save money on compensation.
"BA did not respond to our latest proposals before cancelling these flights.
"Passengers who will be affected by these cancellations should know that we have given BA multiple opportunities to work with us so we could call off this action."
When BA cancelled flights ahead of this week’s walkout, many passengers complained about difficulties contacting the airline, while some were sent cancellation emails in error.
The airline said it had added extra staff to its customer relations teams and had up to 900 people answering phones at peak times.
It had dealt with 491,000 calls and 125,000 tweets since the strikes were announced last month.
Balpa alleges the strikes cost BA more than £40 million a day, when the dispute could have been settled for £5 million.
Adam French from consumer group Which? said: “British Airways must learn from its recent mistakes and not repeat failings that left many passengers’ travel plans in tatters if it has any hope of recovering from this mess and regaining the trust of its customers.
This is amid growing dissatisfaction over airline, after technical glitches earlier this year left thousands of passengers across London airports.
Despite promoting itself as a premium carrier, BA was rated almost as unpopular as budget airline Ryanair this year.