Anti-worker Union supports high ranking supervisors instead of rank-and-file employees

I work in a government office as part of the head of office's legal staff. Recently, I was assigned the task of preparing memos, warnings, and other admin/discipline-related documents for erring supervisors. One of those supervisors was a division chief who, instead of explaining as he was asked, decided to verbally assault me, insult me, and try to intimidate me. Now our own union is protecting the division chief and excluding me.