FWIW in the UK it's a legal right not to join or support unions (closed shops are outlawed), and unions can't charge non-members dues (no agency shops either). Lots of people (both company-owners and ordinary citizens) have problems with them anyway. Somebody in my industry recently left the union angrily and publicly, then subsequently criticised the union for not representing their interests after they'd gone. There's no accounting for folk.
Yes, the UK has never been a place with strong freedom of speech and contract protections, so it makes sense they would outlaw business owners from voluntarily entering into security clause agreements with their employees.
