Alright as someone who has seen this happen... Don't. Fist off, if the employee doesn't already know what the benefits of a union are and how to go about organizing one, this does nothing to change that. Second, it puts them in a dangerous position with management. Obviously, any good Union drive should be fully prepared for union busting tactics, but ideally you want to keep that shit secret from management for as long as possible. And imagine how frustrated you'd be if a customer pulling a stunt like this got you fired.

Instead what you want to do is talk to your family, friends, and coworkers about what a union can do for them and talk about how to effectively organize a union drive. Make sure that shit is led by the workers, and puts forward strong demands and escalating tactics. They should also absolutely get community support, but in organized, meaningful ways - think things like mailing lists to get the word out about rallies, boycotts, etc.

Unions are hell of a tool and they should be organized in the most effective possible ways.