The US Environmental Protection Agency has unveiled a final rule for regulating major emitters of greenhouse gases.

Under the Clean Air Act, starting July 2011, sources of at least 100,000 tonnes of emissions a year and any existing plants that increase emissions by 75,000 tonnes will have to seek permits, the agency said.

This will affect some 15,550 polluters such as coal-fired plants, refineries, cement manufacturers, solid waste landfills and others. The final rule is a revision of the rule proposed last year, which was to apply to emitters releasing at least 25,000 tonnes a year.

“What we realized at the 25,000 level was that we were going to be actually reaching sources that we did not intend to reach,” Gina McCarthy, the EPA’s assistant administrator, told The New York Times on Thursday. She added that the rule would apply to sites accounting for about 70 percent of the nation’s greenhouse gas emissions.

The EPA got involved in regulating emissions last year, after it said that carbon dioxide and other greenhouse gases pose a threat to human health and welfare. Under the Clean Air Act, this gives it authority to regulate emissions.

The Obama administration made clear that the finding was intended to goad Congress into superseding the agency and adopting emissions limits of its own. The rule today comes a day after a climate and energy bill was introduced in the Senate, one that would effectively shift regulatory power over greenhouse gases to Congress.