RAT 5 wrote
They should publicly declare they will never set foot on an a/c where zero hour contracts are in force. That would be credible, not this blind eye action.
Even better, pull their AOCs, landing rights, take them to court for undermining EU wide minimum employment and social regulations standards.
Not so long ago a well known European business jet company went bust for this very reason. Faced with back-charges and penalties in the millions for their failure to properly register and pay social security contributions for their pilots they had to declare bankruptcy.
It is just as easy to prove that pilots working at an airline in scheduled services do not qualify as entrepreneurs: not free to charge as they want, not free to offer their services to who they want, not free to decide their work hours, under complete direction on how to fulfill their 'services' down to the letter, etc.
I wish I was a lawyer, lots of money to be earned hanging those companies and authorities out to dry.