British Airways has canceled almost all its flights for 48 hours, affecting as many as 195,000 travelers, due to a strike by pilots over pay.
The U.K.'s flagship carrier said in a statement Monday that it had "no way of predicting how many (pilots) would come to work or which aircraft they are qualified to fly."
As a result, it said it had "no option but to cancel nearly 100%" of its flights for the duration of the strike.
British Airways operates up to 850 flights a day. London's sprawling Heathrow Airport was most affected by the work stoppage as it is the airline's hub and is used for many of the company's long-haul international flights.
The sprawling departure area at Heathrow Terminal 5 was almost empty, with only a handful of BA flights set to leave on Monday.
There were no queues at any of the check-in desks or security gates and only a handful of people waiting on benches. The terminal is typically quite busy.
British Airways said it stands ready to return to talks with the pilots' union, Balpa, and that it has offered all affected customers full refunds or the option to rebook. The airline had been preparing for weeks for the strike, giving travelers advanced notice.
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"We understand the frustration and disruption Balpa's strike action has caused our customers," it said.
"After many months of trying to resolve the pay dispute, we are extremely sorry that it has come to this."
British Airways says it has offered pilots an 11.5% pay raise over three years but the union says its members want a bigger share of the company's profits.
The union accuses British Airways of making big profits at the expense of workers who made sacrifices during hard times. British Airways' parent company, IAG, made a net profit of 2.9 billion euros ($3.2 billion) last year.
Union leader Brian Strutton said pilots are determined to be heard.
"They've previously taken big pay cuts to help the company through hard times. Now BA is making billions of pounds of profit, its pilots have made a fair, reasonable and affordable claim for pay and benefits."
A further strike is penciled in for Sept. 27.