Why can't you strike? You can do whatever you like.
Just to back up what Maz and others have said.
In the UK if your company leaves you and your cohort's (e.g. current easyjet pilots) T&Cs alone then carrying out Industrial Action (IA) in protest over another group's T&Cs, ( e.g. sub-contractors, flying for Easyjet and provided by a third party ) would be extremely ill advised.
If do proceed to IA you'll face:
1. a legal injunction,
Followed by, if you strike anyway because you think "you can do whatever you like":
2. Confiscation of Union Reps assets, confiscation of Union assets, dismissal of all employees who took part and/or organised the illegal industrial action, and no doubt a list of heaven knows what else.
BALPA found this out the hard and expensive way when BA pilots threatened to strike over the T&Cs of prospective "Open Skies" pilots a few years back.
I appreciate in some countries it's possible to strike at the drop of a hat, or at least with minimal warning, over just about anything that upsets the union membership from the colour of uniforms to management bonuses but in the UK Unions are stuck with some very draconian legislation regulating their behaviour.