The centerpiece of Gov. Tom Wolf’s plan to fight climate change will confront its last regulatory hurdle today, in a fight pitting Democrats, nuclear power plant owners and the renewable energy sector against Republicans, fossil fuel-plant owners, blue-collar labor unions and heavy industry. The plan to impose a price on carbon dioxide emissions from fossil fuel-fired power plants in Pennsylvania is going before the Independent Regulatory Review Commission, a five-member panel made up of three Democratic appointees and two Republican appointees.