The U.S. Supreme Court ruled Monday that the Environmental Protection Agency made a mistake when it told electric power plants to reduce mercury emissions. The high court says the EPA should first have considered how much it would cost power plants to do that.
The decision comes too late for most power companies, but it could affect future EPA regulations.
Mercury in the air is a health risk. When you burn coal or oil, you create airborne mercury that can end up in fish we eat and cause serious health problems.