PORTLAND – Four men have been arrested after an undercover investigation into illegal distribution of the prescription drug OxyContin in Portland.

Paula Silsby, the U.S. attorney for Maine, said in a statement that one of the men works for the city of Portland.

She said that at the time of his arrest, Richard Foster, 41, was selling the prescription painkiller while operating a sidewalk sweeper on Brighton Avenue in Portland.

Foster, of Otisfield, and Ray Pottle, 47, of Windham are charged with possessing oxycodone with the intent to distribute it. Richard Smith, 43, and David Hanks, 42, both of Windham, are charged with distributing the drug.

A spokesman for the city of Portland said Monday that Foster has worked in the maintenance department for at least 12 years. Officials will decide after an investigation whether to put him on administrative leave.

The men appeared before a federal magistrate Monday afternoon. If convicted, they face 20 years in prison and $1 million in fines.