Been working at my job for 3 years, part of a union, my employer is trying to fire me and said I didnt sign my employment papers 3 years ago

I work at my job for 3 years My boss wants to fire me Usually we go through a union and its almost impossible to get fired unless you massively mess up a billion times They informed me that apparently 3 years ago, after probation, i didnt fill out my employment forms so I never got my real employment status I feel like since I worked there for 3 years I am still entitled to the same treatment as other employees Thoughts ?