John Gilbert, a board member of Electric City Power, said he resigned because doctors found a tumor in his bladder. He said he underwent surgery two weeks ago for what he called a treatable and non-life-threatening condition, but given his state, he would not have time to continue serving on the advisory board.
Board meetings for Electric City Power have drawn criticism, in part, because of the city's involvement in a proposed coal-fired power plant east of Great Falls.
Power plant developers now may build a natural gas-fired power plant instead after environmental groups protested.
The city's efforts to sell public power also prompted some criticism from residents.