unfair performance standards

I have been working for a transportation company as a part time courier for roughly two years now. As couriers we have to make a certain amount of stops in a specified time, but the number of stops are specific to particular routes. Most of us part timers do "extras" past our scheduled route. For example,we help other couriers or just deliver one piece across town. Some time ago, the company decided to judge the performance of their part time couriers past their scheduled routes. Unfortunately, this had an detrimental effect on the the part timers. Since we are often doing extras and not particular scheduled routes, our performance numbers often look pretty bad. I had discussed the issue with my manager twice. My manager had always stated that he would ignore the numbers past my scheduled time. Yet he never does. Recently, the regional manager had stopped by to tell us all that from now on everyone must achieve a certain goal (impossible for most part timers) or there will be terminations. Well, he didn't exactly use those words, he was rather vague, but in round-about terms that was what he got across.
I also found out that another courier under a different manager doesn't get judged by the "extras" she does past her scheduled route.
I am considering drafting a document that will clarify my position about the current situation and requesting a meeting with my manager to discuss the document. I just want to produce a paper trail that somehow states that I find the performance standards unfair and unacceptable for such and such reason. I am not sure what else to do...contact an attorney and ask for how to proceed from here.

Paper Trails are important and necessary. It would be smart to meet with an attorney who could look at your employment contract, employee handbook and any and all paperwork pertaining to your situation.

The attorney could then help you draft a letter that hopefully has the impact that you are looking for.