"Arranged as a members-only union, the new organization won’t seek collective bargaining rights to negotiate a new contract with the company. Instead, the Alphabet Workers Union will only represent employees who voluntarily join, as reported by the New York Times. That structure will also allow it to represent all employees who seek to participate — including temps, vendors, and contractors (known internally as TVCs) who would be excluded by labor law from conventional collective bargaining."

That sounds to me awfully like a voluntary union, though I'm not familiar with the laws allowing unions in various US states to compel non-members to join.