The California Fair Political Practices Commission is looking at campaign material distributed in the March election.
At issue is whether any officers were pictured in uniform on campaign material. If they were, that would be a violation of state law and the union could be fined $5,000 for each offense.
The city has completed its own investigation. Interim chief administrative officer Pedro Carrillo told the Los Angeles Times that he cannot disclose results of the investigation because it's a personnel matter.
Voters recalled remaining council members during the March election in the scandal-plagued city of about 40,000.and union-backed candidates were elected.
The Police Department viewed the election as a fight for survival in the financially strapped city.
The Associated Press contributed to this story.