labor union office
Administrative space designated for a union representing the interests of a group of workers.
A labor union office is an administrative space especially designated for use by a union representing the interests of some group or class of workers. Normally this usage is assigned to places either owned or exclusively rented by a union; labor unions may also occupy regular commercial office space.
The office accommodates the work of the union as an organization. A workplace employing union members is not itself a union office unless it also contains that administrative function.
Union ownership and exclusive rental are usual arrangements, but administration can also occupy ordinary rented commercial space. The union's work is distinct from the employer's business administration.