I also got the letter due to my Iberia Plus account where I credit Avios from my c/c, petrol,...because actually I fly with IB very few times(practically no short haul routes ex Bcn).
The main problem for Iberia are the ridiculous high salaries, low productivity and benefits of their pilots. On top they consider themselves as an untouchable aristocracy that can put the company on its knees every now and then.
I hope that in this occasion the pilot union(Sepla) cannot get away without sacrifices.