Without a due process ensured by a union, it’s very hard to know what they did.
Even if someone does something truly horrific, unions still need to protect their rights to a proper hearing, evidence, etc.
A while ago a reporter was fired from the NYTimes for repeating racist language used by a third party.
The reporter had works at the NYTimes for decades with a clear record. A few years before the incident, they became part of unions negotiating team.
Once they joined the negotiating team, the paper suddenly began disciplining then for minor infractions.
Once the allegations about racist language came about, they had a dirty record.
Per the union agreement, had a right to see the evidence against them. The paper refused to do that.
If this person hadn’t been part of union negotiating team, they would have had a clean record, and likely would have survived.
They are now working as a reporter at the Economist.