Pink slips for union backers: a $775k mistake.

While it's legal to make your case to employees why they're better off without a union, you need to know how far your anti-union efforts can go.

The National Labor Relations Act says you can't discriminate against union supporters, promise them certain benefits to abandon the union or prevent pro-union solicitation during nonworking hours or breaks. Also, firing employees because they support the union is an obvious no-no.

Recent case: A Silicon Valley software start-up agreed to pay $775,000 for firing 15 software engineers--all of its nonmanagement staff--after they attempted to secure union representation by the Communication Workers of America. The actions...