It is fundamentally oppressive and undemocratic to deny free men the chance to voluntary come together to collectively set the prices for the services they're selling.
This collective bargaining is called price-fixing.*
This isn't a clear-cut issue of rights that can be settled on principle. Workers have been given the right to collectively fix prices through unions not because it's a fundamental freedom, but because it has been recognised that employees negotiate from a position of relative weakness to their employer.
This collective bargaining is called a union.
What is your problem with a group of people choosing to organize this way?