I feel completely comfortable with my employees working on side projects, learning new things, and ask them to update their resumes at least once a year with whatever new skills and tasks they have picked up recently. I WANT them to feel like they don't depend on me, because them not feeling tied to me and their job actually keeps us on friendlier, more open, and more even terms, and keeps the business more productive and innovative. If my employees were in a union, or had some sort of control over keeping their job against my will, the work environment would have been a lot more stressful, with "me vs you" tensions rising often.
Suppressing a voluntary union is asserting dominance. I don't support mandatory unions, but trying to eliminate all unions is effectively bullying your employees.