And if the union has enough power and its members care enough, they can say "stop doing that or we'll all quit, good luck replacing us". If the employer has the power to say "go ahead and quit then", then the union doesn't actually have the power to effect change, so why should anyone bother being a member?
> And if the union has enough power and its members care enough, they can say "stop doing that or we'll all quit, good luck replacing us"
How would the union know what the boss tells his new hires? Unions don't get to monitor the hiring process of every communication between a worker and his employee.
First, because the union could negotiate that as part of their initial agreement with the company: "don't use any means to entice or threaten people into not joining the union". If it's that common a tactic, that would presumably be a standard part of a union's playbook.
As for how they'd know it was going on: it only takes one person to "leak" that information to the union. And if the union and company are large enough that new people get hired regularly, they might occasionally find someone who fits the profile and send them through the hiring process specifically to find out how a new employee gets treated.
Are you attempting to make a counterargument, or are you hoping people will read your comment and go "yeah, corporations bad, down with corporations!"? Yes, voluntary unions have to fight against the ability of a company to simply fire people; they depend on the willingness of the entire group to stand together and take the risk together, win or lose.
The whole point of a union is that employees have more power collectively than individually. A company can just tell an individual "no". If all or almost all employees get together and say "the situation is so bad that we're willing to quit (and make a lot of noise and bad PR for you) rather than let this go on", then that's harder to ignore. If the company is willing to fire everyone and deal with the bad PR, and that's cheaper than the union's demands, then the union doesn't actually have the power to effect change even as a collective.
I don't see any reason that either the company or the union should be artificially given more power in that scenario.
Except in the current scenario, the company already has disproportionately more power. A company can get by shorthanded for a while. A person not having a job, however, is far, far more devastating, especially if that person has a family to support.
"Want to receive a bonus at the end of the year, don't join the union".