BY KAVERI NITHTHYANANTHAN

LONDON”The union representing British Airways PLC’s cabin crew on Friday announced that strikes will take place later this month after the U.K. airline and union leaders failed to reach a last-minute deal on changes to working practices.

Unite, the union representing cabin crew, said its members will begin a three-day strike March 20 and a four-day strike beginning March 27.

The decision to strike likely will deter passengers from flying with BA over the period and potentially again in the future, while also adding to BA’s troubles. The company in February reported a pretax loss in the three months to …