British Airways was forced to apologise on Saturday after wrongly telling customers their flights were cancelled.
It came after tens of thousands of holidaymakers' plans were thrown into disarray when BA pilots confirmed they will strike for three days in September.
The airline sent emails to some passengers with flights on non-strike days which advised them to rebook or get a refund.
But it later emerged that the flights had not actually been cancelled and the emails had been sent due to an "error".
A BA spokesman said the company was "sorry for any confusion and inconvenience this has caused".
Passengers described the situation as a "complete mess" and complained they had unnecessarily spent extra money booking new flights.
Within hours of the British Airline Pilots' Association (Balpa) announcement BA sent out emails overnight warning flights on September 9, 10 and 27 would be hit by a "large number of delays and cancellations.”
However, many flights scheduled for the days after the industrial action have also been cancelled because of the knock-on effect on crew staffing levels at the company. As a result the action could see disruption to services over at least five days.
BA's customer service lines were jammed on Saturday morning as travellers who awoke to the news of the strike tried to find alternative arrangements.
The company's Twitter feed was also inundated with messages from frustrated customers, with some complaining they would miss weddings and honeymoons.
In a statement, the company said: “It is completely unacceptable that Balpa is destroying the plans of tens of thousands of our customers with this unjustifiable strike action."
“A day of strike action will cost BA around £40 million," the union said. "Three days will cost in the region of £120 million.
"The gap between BA's position and Balpa's position is about £5 million.
"Our proposal remains on the table should BA wish to reach agreement prior to strike action."
Customers began receiving emails that began: “We are very sorry to tell you that due to industrial action by British Airways’ pilots union, BALPA, your flight has been cancelled.”
Peter Dempsey, 41, said his family could be forced to pay hundreds of pounds for alternative flights for a family wedding in Seville, southern Spain.
"It's the return that has completely screwed us up as we are flying back with our in-laws and we cannot move the dates," said Mr Dempsey, who flies out on September 5 for his wife's cousin's wedding.
"We have no option but to completely cancel both legs and rebook or they won't give a refund."
He said himself and three others were booked on the return journey, on September 9, adding: "I'd estimate we will be about £200 out of pocket.
"Not a massive amount but not everyone has that kind of money. God knows what it is costing others who have flights to America etc."
He said they spent £550 on their flights but to return on easyJet would cost £330, or to rebook with Ryanair roughly £200.
Mr Dempsey described the service since the announcement as "shocking", adding BA "clearly don't have enough people to handle such a crisis".
Others complained about a four-week wait for refunds and said bookings on their flights were still listed for sale online.
The airline added: "We will do everything we can to get as many people away on their journeys as possible.
"However, it is likely that many of our customers will not be able to travel and we will be offering refunds and re-bookings for passengers book on cancelled flights."
It said flights with BA CityFlyer, Sun-Air and Comair were not affected and it was "exploring options to supplement our fleet by using aircraft and crew from other airlines".
BA will also work with its partner airlines to schedule larger aircraft.
Chief executive Alex Cruz said the pilots had been offered an "incredible, inflation-busting deal" which would take a captain's pay to over £200,000 a year and they had been "very badly served" by their union.
Bapla said: "Over recent years BA pilots have made sacrifice after sacrifice to assist the company such as taking a pay cut, productivity increases, closing the final salary pension scheme, giving up annual leave days, a new rostering system, and reducing flying pay.
"In what is British Airways' centenary year, this will be the very first time its pilots will go on strike. They do so as a last resort and with enormous frustration at the way the business is now being run.
"Our ballot is valid until January, and more dates may be announced until such time as this matter is resolved."