You're answering a question that wasn't asked so you can bring your view on unionization into the conversation. The implicit question is whether management should, not whether they can.
It's about power to affect change in an organization. The more power you have the better systems you can establish and sustain. Unions should be brought up constantly in these threads about AI mandates and "leadership" directions.
Unions might not be the best solution, or the most practical. I'm all ears for better ways to fight back against bogus leadership. How else can software developers advocate for their interests in an environment where their power is sharply declining (non performance based layoffs, "performance" based layoffs, reduction in junior hiring, reduction in in-office perks, reduction in total comp, etc)?