Looks like IAG are playing hardball....

British Airways has already started cancelling flights after pilots voted to strike for better pay and conditions next month, disrupting travel plans for tens of thousands of passengers.
Yesterday pilots' union Balpa confirmed a strike by more than 3,000 pilots for next month after talks with BA broke down.
By the evening affected passengers had started receiving emails telling them their flights were cancelled, apologising for the inconvenience, and warning them not to go to the airport.
BA wrote: 'We are very sorry to tell you that due to industrial action by British Airways’ pilots union, BALPA, your flight ... has been cancelled.
'The strike is expected to have a significant impact on our operation and will result in a large number of delays or cancellations.
'Please do not go to the airport, you can rebook or refund your cancelled flight online.'
A month after announcing its members had voted for industrial action, the union said there was now 'no prospect of any further meaningful talks' and claimed it had 'no choice but to call this action'.

https://www.dailymail.co.uk/news/article-7389433/British-Airways-starts-cancelling-flights-HOURS-pilots-union-announcing-strike.html