This question already has an answer here:
Can a TV Broadcaster legally refuse to air Political Ads under FCC rules & precedent governing political advertising if a registered political candidate or PAC were to air perceived negative political ads that do not align with it's editorial political leanings?
Example: Fox News (initially did) refused to air Tom Steyer's needtoimpeach.com Ads citing "Negative viewer reaction"
"Due to the strong negative reaction to their ad by our viewers, we could not in good conscience take their money" Washington Post Article
The question specifically asks about Political Advertising by or in support of an Election Candidate. Unlike the Tom Steyer Ads that may or may not be considered Election Ads therefore may not be bound by Election Ad rules. This is a purely neutral question about the law, not loaded or biased to any side since this can affect any candidate or network regardless of party affiliation or partisan bias.