The British Airline Pilots’ Association (Balpa) on Monday commenced a 48-hour strike in a dispute over pay.

Balpa said almost all British Airways flights, totalling hundreds, were cancelled and an estimated 195,000 customers would be affected.

The association said 8.50 a.m. scheduled flights were cancelled, and passengers would be offered a refund or a later flight.

The strike has been labelled one of the biggest in the airline’s history.

Balpa added that a one-day strike would cost the airline about £40 million  ($49 million).

In July, the pilots declined an offer by British Airways of an 11.5-per-cent pay rise over three years.

However, British Airways chief executive Alex Cruz urged Balpa to continue talks to end the strike.

“The discussions must continue, they must be unconditional,’’ he told the BBC.

The management of the airline said in a statement on its website “we understand the frustration and disruption Balpa’s strike action has caused our customers.

“After many months of trying to resolve the pay dispute, we are extremely sorry that it has come to this.’’

London’s Heathrow airport will be worst affected as it is British Airway’s busiest hub.

Balpa’s general secretary Brian Strutton said “British Airways has to wake up.

“Pilots had to accept significant pay cuts during difficult times, and now that the airline was making money, it should give something back to its pilots.

“It is time to get back to the negotiation table and put together a serious offer that will end this dispute.’’

He announced that a second strike is planned for Sept. 27.