The law on strike discrimination and punishments is very clear and an Employer can never discriminate legal strikers for their legal strike action, directly or indirectly. Otherwise the legal right to strike is obstructed
I think you overstate the case. Your employer does not pay you for days you are on strike, is this then discrimination?
None of these things are as black and white as we would like them to be - if they were then Barristers would be paupers. Now there's a dream we can all hold in common