I think I was discriminated against. Can you please tell me if I have a case?

I was put on probation and I ended up being late to work.  They pulled me into a room and demoted me at the end of the shift.  Told me that I was going to be the example even though they haven't followed their own rules until now.  Demoted me and said that as of Monday i will be put on the line.  I showed up to work on Monday and I was told by the coordinator which line and station to go to.  I get to the station and I was approached by a colleague in the same position as i was.  That person was not informed about me and neither was anyone else so I was ambushed with a bunch of people asking me questions about what happened and why.  I not only feel embarrassed but humiliated as well.  I was under the impression that anything that deals with me would be private information and i just don't understand why they even put me in a room to demote me if they were going to do what they did.  Can you help me?  Is this discrimination?