I hear the worst offenders of union busting love to call in consultants or whatever have you when they catch a single whiff of a chance that their workers are thinking of unionizing.
So start spreading rumors your co-workers are going union. Even if they aren't.
Management freaks the fuck out, pulls the chain, calls in the union busters… wastes their time, energy, and money trying to bust a union that isn't even forming.
Then do it again.
And again.
And keep doing it.
Forever.
One of a few things happens – they keep wasting time, energy and money, or they stop believing there is actually going to be a union forming and ignore any such rumors. The former is good (and hilarious) because it means they're wasting money and time and energy.
The latter is better, because it means you can then ACTUALLY unionize in peace, which would also be hilarious.