Members of BA's "mixed fleet" cabin crew began their strike on Saturday at the start of the peak summer travel season, forcing the national flag-career to use nine Qatar Airways planes to cover its flights.
The crew members have been in conflict with the airline since last year over wages. Unite the Union, the largest trade union in the UK, has described BA wages as "poverty pay."
The average mixed fleet employee earns £16,000 ($20,447) annually.
Unite said the walkout, the longest stand-off in the row, is also a response to sanctions on union members involved in previous strikes.
There have been 26 days of strike action so far this year. Unite said that 1,400 mixed fleet members who had been on strike previously had seen bonus payments and travel concessions removed.