I think they're just analysing the effect of a company-focused union versus a wide-spectrum union. I don't think they're implying that there should be only a si

I think they're just analysing the effect of a company-focused union versus a wide-spectrum union. I don't think they're implying that there should be only a single union per company (it's probably not common in the US but that's common in other countries like Germany and pre-Thatcher UK).