Do workers have a right to unionize? If a legislature changes the law to remove collective bargaining, does that deprive workers of their rights?
It depends. It depends on which rights you're talking about and on which rights the law covers.
There are two kinds of rights. The first kind is negative rights. Negative rights either permit you to be inactive or require someone else to be inactive towards you. For example, free speech is a negative right. It allows you to speak, or not, as you choose. It requires the government to be inactive whether or not you speak: the government may not force you to speak and the government may not prevent you from speaking. The right to a free press is another negative right. The government may neither force something to be printed in the press nor may it prohibit the press from printing something.
The second kind of rights is positive rights. Positive rights either require you to be active or require someone else to be active towards you. For example, universal education is a positive right. The government requires you to attend a school of some sort and the government requires someone to provide a school for you. Generally, the government directly provides schooling by forcibly requiring citizens to pay taxes and then using those tax dollars to pay for a school. The "right to health care" is another example of a positive right. If you are unable to purchase your own health care services, the government requires someone else to purchase them for you.
The positive right is distinguished from the negative right in that it requires you -- or someone else -- to be active. It places a burden on you or on someone else. Very broadly speaking, negative rights force others to stay out of your way, as you live your life and make decisions. Positive rights force others to provide for you (as needed), as you live your life and make decisions.
How does this apply to labor and labor law? Well, unions can either benefit from negative rights or positive rights. Under negative rights, individual workers are free to negotiate directly with employers for their pay and benefits. They are also free to associate with other individual workers and form a bargaining group. They are then free to attempt to negotiate as a group, for pay and benefits. They can invite others to join the group at any time and workers are free to leave the group at any time. The guiding rights principle is inaction: no worker can force another to join nor prohibit another from leaving.
Likewise, employers are free to negotiate with the group or to choose to negotiate with workers individually. Once again, the principle is inaction. No employee can force the employer to negotiate with the larger group. Likewise, no single employee can force the employer to stop negotiating with the larger group.
The negative right to labor allows both the worker and the employer to negotiate individually or through a group, whatever they both prefer. It prevents either side from coercing the other side.
Under positive rights, individual workers are not free to negotiate directly with employers for their pay and benefits. They must only negotiate as part of a larger group. All new workers must accept what the group has negotiated and must only negotiate through the group. No worker may negotiate individually as long as he stays in that job.
Likewise, employers are not free to bargain with individual workers. They must negotiate (active principle) with the group. They may not negotiate with any other group of employees -- only with the original group. If the group of workers stops working (goes on strike), the employer may not seek out other groups of employees, to see if they would be willing to work for the original conditions, pay, and benefits. This gives the group a monopoly control over the employer's supply of labor.
The positive right to labor forces both the worker and the employer to negotiate only through a group. It actively forces both sides into a specific association.
In Wisconsin, public employee unions are an example of labor law under positive rights. Employers are required to negotiate with the appropriate union and forbidden to negotiate individual contracts with workers. Employees are not required to join the union but they are required to pay all union dues that union members have to pay and are required to abide by the terms of the current collective bargaining agreement.
Take, as an example, an individual with a PhD in history who would like to work as a high school teacher in Madison's public schools. Under the terms of the collective bargaining agreement with Madison Teachers Inc, the school district must pay that teacher a minimum annual salary of $41,036. (I think. The exact details of the salary portions of that agreement are not entirely clear to me.)
For most employees, this is probably a good thing. Most employees are eager to get the maximum possible salary. Most employees probably feel that even this salary is too low and that they deserve more. But that's most employees in most scenarios.
Consider an alternate scenario. What if the district can't afford another teacher at that level? The teacher may wish to work for less, in the interests of having a job. (Or, he may have other income to live on and may wish to take the job for less in the interests of melding the bright, young minds of tomorrow.) But he's not free to work for a different salary and the school district isn't free to pay him a different salary if he requests it.
Consider another alternate scenario. Consider a worker who does not agree with the political stance of her union, preferring different political goals and outcomes. Under current law, she is forced to contribute union dues to that organization anyway. (For a Wisconsin teacher, this can be $700-1000 a year.) Each year, she is forced to watch as the union gives that money to politicians that she disagrees with and uses that money to oppose politicians that she does agree with. Her co-workers' positive rights to her union dues limit her negative rights to support candidates that she agrees with.
The positive rights to a union limit an employee's negative rights to decide what terms to work under and what to support. I value negative rights far more highly than I value positive rights. For that reason, I believe unions do not increase the rights of the workers, they decrease them. I favor modifying labor law to restore workers' negative rights.