> Wikimedia Foundation is asking for an election to ensure everyone actually wants this.

Why? Does recognition entail that every worker is compelled to join the union?

My dad worked for the United States Postal Service for decades. He never joined the union, but he was still legally required to pay union dues, and the union was still legally required to represent him. So at least in some cases, yes, starting a union does affect all employees and practically requires them to "join" even if there's an option to not join on paper.