Police recorded the incident as a possible assault report. Prosecutors declined to press charges, citing a "lack of corroboration" for Flores' story, said D.A. spokeswoman Farrah Emami.
"I am grateful for my name being cleared of the accusations by union activist Joel Flores," Mensinger said Wednesday.
Flores is a member of the Newport-Mesa teacher's federation, which is unaffected by the city's planned layoffs.
Mensinger said he did not touch Flores between races at a community fun run last month. He said his jacket may have brushed the teacher as he turned away from him after being confronted.
A witness told the Daily Pilot that the two men exchanged words, but there was no physical contact.
The councilman said he believes Flores trumped up the accusations because of their political differences. Orange County organized labor officials deny their group was behind the confrontation, though they have voiced support for Flores' actions that day.
"It is unfortunate that union officials resort to smearing council members' names to further their cause," Mensinger said. "Make no mistake, this will not dissuade me from balancing Costa Mesa's budget. Events like this illustrate why our community must reform the mechanisms that give unions so much power to disparage average citizens and intimidate future leaders from engaging in government."
Flores maintains Mensinger physically pushed against him, and criticized how the city handled the incident. Mensinger was given a copy of the police report the day after the incident, which police later apologized for.
"To me, this just shows that Mensinger and the City Council have contempt for the average residents' opinions," he said. "And they would like us to make it all about 'I'm a union official,' but I'm a resident of this city, a husband and a professional educator who takes pride in what I do. And I'm ashamed of Mensinger and the City Council."