The Employment Relations Authority has deemed a boss' slap on the bottom of his female employee was a "fun slap".

In her finding, Employment Relations Authority member Anna Fitzgibbon says the slap was inappropriate and should not be repeated, but was not sexual harassment.

She says it occurred in the context of a joke, with the woman being cheeky about her boss's floppy hat - and he responded with what she accepts was a "fun slap" on the bottom.