For whatever reason the implication is that "one of them must quit". It's not clear why that is necessary beside (and this is a big one) it being an HR issue, which implies that people cannot operate within proscribed behavior at a workplace --which to me seems goes against people's right to work, but given this implication (where one of the couple must quit) a rational couple would choose for the one with more earning potential to stay and the one with less earning potential to leave. But that also assumes that the one staying would not have greater earning potential elsewhere.
