The U.S. Environmental Protection Agency is beginning to regulate greenhouse gas emissions from energy plants and factories despite vows from Republicans in Congress to stop or slow the regulators.

President Barack Obama, who has pledged the United States will cut the emissions 17 percent from 2005 levels by 2020, wants Congress to pass limits on the gases blamed for warming the planet. There's virtually no chance that will happen before Obama's first term ends in 2012, so he has pushed the EPA to move.

The EPA paved the way for the rules in late 2009 when it declared greenhouse gas emissions a threat to human health.

But Republicans, who are taking control of the House of Representatives and who gained seats in the Senate, want to stop or delay the EPA from acting. They say the regulations will hurt job recovery in states heavily dependent on coal, oil and natural gas.

Here are key dates for EPA regulations on greenhouse gas regulations.

JAN. 2 TO JUNE 30, TAILORING RULE

Power plants, oil refineries and factories that emit at least 75,000 short tons per year of greenhouse gases, and that are required to get permits for other pollutants, must now use the so-called best available control technology, or BACT, when expanding or doing major retooling.

The EPA hopes this will push plants to cut emissions through energy efficiency.

Under the Clean Air Act, too many greenhouse gas sources would have to be regulated under a general rule on the pollution so the EPA "tailored" the law, meaning they are applying it to only the big emitters.

In addition, big plants that are required to get permits to emit traditional pollutants that cause smog and acid rain, also need for the first time to get permits to emit greenhouse gases.

MARCH 31, 2011, DISCLOSING EMISSIONS

Large polluters will have to submit annual reports to the EPA about their emissions by March 31, 2011. The polluters have been required to measure the emissions since the beginning of 2010. The rule covers global warming pollutants including carbon dioxide, methane and nitrous oxide.

JULY 1, 2011 TO JUNE 30, 2013, TAILORING RULE PART 2

Any source that will emit at least 100,000 short tons per year must obtain the permits for both BACT and for polluting greenhouse gases even if they have not had to get permits for other pollutants.

STARTING IN JULY, PROPOSALS ON EMISSIONS STANDARDS

In addition, the EPA will propose performance standards on greenhouse gas emissions for both new and existing plants starting in July for power generators and for oil refineries in December.

Specifics have not been established on the standards other than that they will require plants to reduce emissions.

The standards will be finalized in May 2012 for power plants and in November of that year for refineries.

2016, SMALLER POLLUTERS?

Plants and factories that pollute less than 50,000 short tons of greenhouse gases per year would not be regulated until 2016, if ever, EPA air official Gina McCarthy said last year.