This study examines how isomorphic mechanisms that are either external or internal pressures of policy diffusion relate to unrequired ethics policy adoption by city governments. The analysis using the secondary data from the 2017 Florida League of Cities’ CityStats Survey and audited city financial statements gathered from the state reveals that the likelihood of ethics policy adoption is greater among the cities that pay their council members higher salaries, have a neighbor city with an ethics policy in the same county, are located in a home rule county, and have a council-city manager form of government. The findings suggest that institutional pressures play an important role in municipal ethics policy adoption, with the memetic external peer pressures most strongly associated with Florida cities’ ethics policy adoption.