An ACMA investigation found that Nine had aired gambling adverts during the pre-game program for games one and two of the State of Origin rugby league series on its 9Now streaming platform.
Australian regulations limit the amount of gambling adverts that can be shown around sporting events, with no adverts permitted within five minutes before a game or event is due to begin.
However, this rule only applies if a broadcaster informs viewers when the game is due to start at least 24 hours in advance. The ACMA said that as Nine did not do this, the rules instead applied five minutes before the pre-game coverage, rather than the match itself.
As such, this placed Nine in breach of regulation and led to the ACMA pursuing action against the broadcaster.