"Unfortunately, with no detail from BALPA on which pilots would strike, we had no way of predicting how many would come to work or which aircraft they are qualified to fly, so we had no option but to cancel nearly 100% our flights."
The statement continued: "We remain ready and willing to return to talks with BALPA."
The airline said it is "offering all affected customers full refunds or the option to rebook to another date of travel or alternative airline." Customers with tickets for Monday or Tuesday should "not go to the airport"; instead, they should rebook or request a refund online or by phone at 0800 727 800 in the U.K. or +44 (0)203 250 0145 outside the U.K., the carrier said.
BA CityFlyer, Comair and SUN-AIR flights are running as planned, according to the statement.
BALPA tweeted Sunday that the airline didn't reply when the union offered a proposal last week that could have prevented the strike.
Pilots plan to strike again Sept. 27, the AP reported.
Read more here.
– The Associated Press contributed to this report.