While the parent companies of NBC, ABC, CBS and Fox are not prohibited from owning a second broadcast network (and all of them, except for ABC, are co-owned with one), an FCC law known as the "dual-network rule" does disallow a single company from owning two or more of the major networks; this came into play in 2019, when ABC's parent company bought most of Fox's assets but was required to leave Fox as a separately owned network.