Johns Creek Mayor Mike Bodker says the accusations against him are politically motivated.
The council voted 5-0 this week to hire the outside counsel.
City Councilman Randall Johnson said the action follows several reprimands of the mayor about what Johnson described as "questionable actions" and concerns that the mayor might have violated the city's charter and ethics ordinance.
The city's charter states that the mayor "represents the will of the Council," Johnson said in a statement.
"However, there have been allegations that he's repeatedly involved himself in actions and situations that were outside the will of council," he said.
The statement did not include specific allegations. Ro
Bodker told WSB-TV that tensions with the council peaked recently over his support of a project the council didn't support -- a proposal to turn an aging bridge over the Chattahoochee River into a pedestrian walkway that would connect a walking and biking trail with neighboring Duluth.
"There's been this tension for a while," he said. "I think the only losers in this situation are the citizens of Johns Creek. It's never good to have these kinds of battles publicly."
Bodker also thinks the conflict arises from the natural tension that occurs between the executive and the legislative branch, he told The Atlanta Journal-Constitution.
"But it gets magnified by the fact that I'm a very forward-thinking, go-getting, strong-personality mayor," the mayor said. "I think that's what the citizens wanted in electing and re-electing me."
Bodker has been the city's first and only mayor since the city northeast of Atlanta was incorporated in 2006.
Attorney Bob Wilson said his firm would be charging Johns Creek $185 an hour to conduct the investigation, and that he hoped to have it completed by August.
The lawyer's report on the matter will be made public once the investigation is completed, Johnson said in the statement.
Copyright 2013 The Associated Press.