I really don't get how a blanket no union-policy is legal? Wouldn't this just deny the workers basic rights (to unionise)? To me it feels like "blanket no minim

I really don't get how a blanket no union-policy is legal? Wouldn't this just deny the workers basic rights (to unionise)? To me it feels like "blanket no minimum wage policy" or "blanket no workplace-safety standards policy". Wether to form a union, and collectively bargain, should be the decision of the workers without any say of the corporations. It really feels to me like "I am sorry about you trying to establish workplace safety standards but we unfortunately follow a global no workplace-safety standards policy and do not agree to minimum workplace safety standards in other parts of the world".