"Who are the workers today?"
Translation:Cé hiad na hoibrithe inniu?
I took lucht oibre as having more of a categorical meaning, and oibrithe as more of an individual meaning — akin to “people” vs. “persons” in English. (For example, the Labour Party in Ireland is Páirtí an Lucht Oibre.) The question above is general enough for “the workers” to take either meaning, so either na hoibrithe or an lucht oibre should be acceptable; since collective nouns are referenced with plural pronouns, iad would be correct in either case.