I am not so sure an airline can remove staff travel privileges from a striker as long as the industrial action is legal.
Safety Concerns,
It does not matter a jot whether the strike is deemed legal or otherwise as far as staff travel is concerned. Staff travel has already been taken away from thousands of BA pensioners who retired in the knowledge that their ST was for the rest of their life. Last year that deal was rescinded, and the period of eligibility shortened to become equal to total length of service.
Some retirees banded together and took very expensive legal advice on the issue. Result: the removal of ST and changes to some of the conditions remain 100% under BA's control.
To be fair, some of the changes have been beneficial, like the opportunity to buy standby for Club, but the fact remains BA have a precedent of successfully remove the benefit.
So, don't be fooled. ST can go, and will go.