The U.S. Environmental Protection Agency released final rules to regulate greenhouse gas emissions from stationary sources such as power plants, refineries and factories.

EPA's new rules in effect "tailor" the Clean Air Act permitting requirements to include greenhouse gases. And by raising the emissions threshold, the EPA regulations are intended to soften the impact on small emitters.

"After extensive study, debate and hundreds of thousands of public comments, EPA has set common-sense thresholds for greenhouse gases that will spark clean technology innovation and protect small businesses and farms," EPA Administrator Lisa Jackson said in a statement Thursday.

Starting in January 2011 under the new rule, stationary sources that are already obtaining a Clean Air Act permit for other pollutants would be required to include greenhouse gases in their permits if they emit at least 75,000 tons of these emissions a year. In July 2012, the rule would expand to include all new facilities that emit at least 100,000 tons a year.

EPA said the rules would cover 67 percent of greenhouse gases from stationary sources. It estimates the regulation would result in 900 permits for both new sources and modifications to existing sources of global warming pollution.

The new rule, in addition to carbon dioxide, addresses a group of five other greenhouse gases: methane, nitrous oxide, hydro fluorocarbons, per-fluorocarbons and sulfur hexafluoride.

The timing of EPA's announcement appeared to be calculated. It came a day after U.S. Sens. John Kerry, D-Mass and Joe Lieberman, Ind-Conn., introduced climate change legislation aimed at curbing the growth of greenhouse gases.

"The Obama administration has again reminded Washington that if Congress won't legislate, the EPA will regulate," Kerry said of EPA's announcement in a statement.

The EPA rules are likely to prompt litigation.

The National Petrochemical & Refiners Association, a trade group, says EPA's new rules are unlawful.

"If EPA wants changes in the Clean Air Act it should propose them to Congress, not unlawfully take on the role of Congress," said NPRA Executive Vice President Gregory M. Scott in a statement.

"If EPA is allowed to get away with this, it sets a dangerous precedent for unelected officials in federal agencies to change laws approved by the elected representatives of the American people," he said.