Perhaps you're confusing it with the Fairness Doctrine. The so-called "equal-time rule" is Section 315 of the Communications Act of 1934 and applies to
advertising by political candidates, not to news broadcasts. Whittled down, it states that all political candidates must be given equal
access to free or paid promotional air time — not necessarily that they must be given air time, period. It does not, for example, force TV or radio stations to take a financial hit if a candidate cannot afford as much air time as an opponent.
In 1959, the law was amended by Congress to include interviews, debates, documentaries and spot-news reports as exemptions along with scheduled news programs. That's why stations and networks can dictate which candidates may participate in debates.
http://www.museum.tv/archives/etv/E/htmlE/equaltimeru/equaltimeru.htm