ANY organized action or drive (other than a NLRB approved strike) which can measureably affect the company in ANY WAY WHATSOEVER is considered self-help and is illegal. This has been upheld many times in the past.

If a union in any way sponsors, encourages, publicizes, or communicates such an action they will be held financially liable for the company's damages.

In fact, if a union fails to take aggressive action to discourage self-help activities, they can still be found liable. This is why unions will usually denounce any such action which they become aware of.

Unions have been fined millions (maybe tens of millions) in the past for this sort of thing.

Individuals who organize these activities could also get fined or fired.