What recourse do I have when a company will not abide by its own severance agreement?

Three years ago I worked for a Fortune 500 company that was bought out. My position was one of several hundred that was eliminated after the buyout. We all signed severance agreements that state we will be considered for re-hire as any other external candidate. However, they are refusing to consider us because we received a severance package. The position I held was recently posted and I was told by HR at company HQ that I can't be considered because I received a severance package. I applied for my old job and to avoid hiring me, they hired someone internally who didn't meet the minimum job qualifications. I was absolutely not terminated because of any performance issues. I know of others who were told the same thing when they applied for entry level factory jobs with very little qualifications required. It was mostly long term employees over 50 who were let go at my facility.

Do we have any recourse - and where should we lodge our complaints?