Yes, there are several unions that cover sales people. The thing is you have to have enough people committed to the cause before the union will come in and sign everyone up. You have to organize and then vote in a union. Employers can't fire you for organizing or joining a union. Of course employers will attempt to intimidate and dissuade people from joining. What is most important is to document everything if you are planning to organize. All conversations, correspondences, documents, phone calls, emails, etc, should be documented and stored somewhere safe, not using company assets. One of the problems in organizing a labor union is that most states maintain at will employment, so essentially a company can fire you, and you can leave for no reason or for any reason. This allows the employer to fire people at will. This could mean that the employer fired you because they believed you were organizing a union, but used another pretense for the firing. This is why its essential to document your every move when you are organizing a labor union. You have to prove that the firing was based on your attempt to organize and not because of the reason the employer states.
If things have gotten so bad that sales people are looking to form a union, I feel bad for the people being subjected to Niznick's abuse. In a normal economy, i.e. 5% unemployment, the easiest thing to do would be to seek another employer. In the current economic environment, unethical employers like Implant Direct abuse and take advantage more frequently because they feel the employee has less opportunity to leave. In the end a business that values their employees, treats them fairly survives. The employers, like Niznick's implant direct eventually fail. At the end of the day its the employees who provide the attributes that make a company successful.