I was told I couldn't bring up Asperger's as a "defense" at my eval/firing unless I had asked for accommodations for my disability when I hired in. But there are probably several differences between your case and mine: I had been hired just 3 years previously (in 2000, fired in 2003). Also, I was often late, so it was very easy for them to build a case against me.

Very smart to request your Union rep. How long have you been working there? How easy would it be to find another job? How do you get your meds, GP or psychiatrist? You may want to contact an employment rights lawyer.