It seems as of late that the company I work for is just trying to get rid of me, for no reason. I work on commission and hit quota every month (with very few exceptions) so its not like I'm not doing my job. But my question is this. I was literally less than a minute late for a conference call the other morning and the regional manager sent my boss an email saying to give me 3 final written warnings just for that one incident, while another employee completely missed her conference call yesterday morning because she was going to a concert. They said nothing at all about the other employee missing, but want me to have 3 final written warnings for that one incident. This kind of thing happens weekly to me, and I'm wondering if this is legal? Also, is this some form of discrimination?

Its legal.. and unless you have a labor contract that's still active, and a Union representing you... they really don't NEED a reason to get rid of you... and if they want.. there is nothing you can do to stop them. However most will look for a compelling reason before they do... as it costs them time and money to hire and train a replacement.

That's why its called AT-WILL employment... you are there at their will... as well as your own... if either party decides your continued employment there is not in their interests... if can easily and simply be terminated.

There is no RIGHT to be employed by any other entity... would someone else have a RIGHT to be hired by you to be your housekeeper or gardener?

They can fire you just because they don't like your personality as easily as you not doing your job as required. And its THEM that gets to decide what is doing the job to requirements and their standards... not you.

I assume you haven't been in the workforce long based on asking this sort of question. But basically... that's life, if you want to call the shots... you can always start your own business. As long as you work for someone else... they get to call the shots.

Yes its legal and while it may be discriminatory, unless you are a protected class, the discrimination is not illegal. I would start looking for another job.

They can do it for many reasons, but can not because of age, sex, religion and the other protected reasons, they may do this , if they just don't like you. If they are doing something like this "every week" then you are doing something minor that this wrong every week??

You commit mistakes every week, and it's natural that your boss becomes annoyed. The girl being tolerated must have some advantage that you don't have, and you should not compare you & the girl in the way you mentioned above.
No, I don't think it's discrimination. Here are some resources on discrimination law and labor law.
Types of Discrimination
2013 OSHA & Federal Labor Law Posters from EasyBusinessPosters