The issue is, you're undermining the rights of your laborer's to organize, and I'd even be willing to make a case that you may be shooting yourself in the foot in the long run, because if you annoy them to the point they organize anyway, you can expext compensation to be elevated even more than it would have been to satisfy the collective bargaining unit since they will pass on the cost of paying for their own organizing infrastructure (since you can't be trusted to let your employees use yours).
So they need to nut up and shut up. If you can't be trusted to let your laborer's organize in good faith, they have no ground on which to stand when the bill comes for a second labor specific communication network comes due.
All that waste they could avoid by just being decent disinterested network operators. Sad really.