So apparently the labor force lost real numbers of union workers, as in there were fewer union workers in 2021 than there were in 2020.

This got me thinking about what a union in a non-manufacturing economy should look like. I understand what it would look like for workers in a factory, or in construction, or in a warehouse setting, as well in some service industry jobs (hotels, restaurants, etc). But for the average American worker who works in an office doing sales or marketing or customer service - what exactly does union representation look like? What are the advantages?