washington u.s. supreme court side obama administration thursday rebuff bid 20 state halt environmental protection agency rule curb emissions mercury toxic pollutants power plant action come month high court put hold federal regulations curb carbon dioxide emissions mainly coal-fired power plant centerpiece president barack obama strategy combat climate change chief justice john roberts deny petition make last week state lead michigan put rule hold federal appeal court decide december leave intact epa reassess cost implement regulation state argue stay necessary supreme court already hold find rule rest unlawful beyond epa statutory authority supreme court rule last june epa consider compliance cost decide limit emissions mercury hazardous air pollutants mainly coal-fired power plant return case appeal court u.s. court appeal district columbia circuit subsequently say regulations could remain place government respond high court june rule appeal court give epa april 15 come compliance cost epa rule go effect last april apply 1,400 electricity-generating units 600 power plant many already compliance epa spokeswoman melissa harrison say agency please roberts action note power plant large source mercury pollution unite state practical achievable standards cut harmful pollution power plant save thousands live year prevent heart asthma attack harrison say environmental group 15 state ask court reject stay request applaud roberts action call attorneys general group state lead michigan end legal challenge rule rule safeguard millions american children poison mercury arsenic acid gas say vickie patton general counsel environmental defense fund anti-pollution advocacy group party case u.s. top court deny bid block mercury air pollution rule