Identify URL Source from link in Form

[Fortuna707]

I have several affiliates that I want to provide a link with a unique ID. When a visitor to a affiliate site clicks on the link and then fills out the form on my site I can identify the unique ID in the form. I need this to track affiliate traffic.

My form link is www.eurekapayments.com/referralID101.php

Thank you in advance for your support and cooperation.

Ron