The flip side is right to slave states. First off, when there is a union in a given industry, even "non union shops" benefit as the wages they have to pay are higher. Secondly, where is the power balance when workers don't have the right to come together as a group to balance the power in labor negotiations?
Even Ayn Rand, if you read her stuff with a clear mind rather than a biased one, believed in unions, just not unions that made unrealistic demands. If you've got a $20-100M CEO and CFO who've done nothing to improve the business, blaming unions is bullshit pure and simple.