One person can join a union. They might, depending on the union, get extra insurance or legal representation or some other benefit not tied to negotiation with

One person can join a union. They might, depending on the union, get extra insurance or legal representation or some other benefit not tied to negotiation with the employer. A one-person strike is generally considered a resignation, though. One core function of a union is as a collective bargaining group. It's difficult to collectively bargain when your collection is one person.