Yes Baggers, it is (though BA will have to pay basic salary on the non-strike days). That's exactly what BA did last time. The loss of allowances over that period will mean the strikers will lose quite a lot of cash, poor dears
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Besides financially penalising the strikers, it will also make flight scheduling far easier for BA once they have derostered all of the strikers and have some degree of certainty over how many staff will be available. Therefore, BA should be able to increase the flight schedule as the strike progresses.