It is a private contract between two private entities, and as long as the government is not forcing companies to make such agreements, it is nobody else's business what the two parties agree upon. If a company finds that it is in a relationship that is disadvantageous, then it can choose not to renew the agreement, close up shop and move, or whatever...
In a recent Reason article, J.D. Tuccille makes a similar argument, discussing it in the context of recent legislation passed by the Michigan legislature. Granted, given the thuggish behavior of Michigan union bosses during the past week, it is hard to find them to be particularly sympathetic figures. This is especially true given than these same union organizers would, in a heartbeat, doubtless use the same power of the state government to mandate closed union shops that was used to ban them. One wishes that the argument could be on a more elevated level, but there you have it.
And of course, public sector unions need not apply for sympathy here at Montana Headlines, since there are a number of missing factors: public entities such as cities and states can't close up shop, move to a more friendly location, declare bankruptcy and dissolve a corporation, or anything similar. Most perniciously, since public sector unions pour large amounts of money into elections for everything from the local school board to the Presidency, there is all too often the unedifying spectacle of having "negotiations" consist of folks on both "sides" of the table be actually the same side.
Those paying the bills -- namely, taxpayers -- are thus left without any representation in the negotiations and are regularly fleeced in the course of such "negotiations." Imagine a situation where in every private business or company, the employees got to choose the board of directors and the CEO, and you'd be seeing a private sector version of what we currently have in the public sector. Businesses would be run into the ground right and left, since management wouldn't be accountable to those who owned the company, but rather to the employees. And indeed, cities and states are being run into the ground financially across the country in precisely that manner.
Ironically, by passing right to work laws, the very unions that have every moral justification to exist (and which are, at least in theory, motivated not to put employers out of business and thus their members out of jobs) are hamstrung, while in those same states, public sector unions simply gain even more power, since they are the only union game in town to bankroll Democratic candidates.