New battle opens on US carbon emissions
The opening salvoes have been fired in a new political battle in the US over greenhouse gas emissions.
Having failed to pass legislation through Congress, President Obama wants the Environmental Protection Agency (EPA) to regulate emissions.
But draft measures before Congress seek to squash the EPA's authority.
Testifying to a congressional committee, EPA chief Lisa Jackson said the bill ran counter to science and counter to a 2007 Supreme Court ruling.
The issue could have ramifications for the UN climate negotiations, with many developing countries looking to the US - as the world's biggest economy - for leadership.
But the politicians behind the new bills cite domestic concerns as the reason for their move - in particular, concern that implementing recently announced regulations limiting emissions from power stations would hurt the economy.
"The EPA and the Obama administration have decided... that they want to put the American economy in a straitjacket, costing us millions of jobs and hundreds of billions of dollars a year," said Joe Barton, a Republican congressman from Texas.
"They couldn't get it through the legislative process… so they tried to do it by a regulatory approach.
"It's not going to work."
And Fred Upton, a Michigan congressman who chairs the Energy and Commerce Committee, said regulation would harm the economy and cost jobs.
"These regulations go after emissions of carbon dioxide, the unavoidable byproduct of using the coal, oil and natural gas that provides this nation with 85% of its energy use," he said.
Mr Upton recently declared that "[President Ronald] Reagan's famous line that 'government is not the solution to our problem, government is the problem' was particularly appropriate in describing EPA's global warming power grab".
But Ms Jackson pointed to the 2007 Supreme Court judgement that said greenhouse gases had the potential to damage human health and well-being and thus fell inside the categories of substances that the agency was empowered to regulate.
"Chairman Upton's bill would, in its own words, 'repeal' the scientific finding regarding greenhouse gas emissions," she said.
"Politicians overruling scientists on a scientific question - that would become part of this committee's legacy."
Meanwhile, researchers at the University of Massachusetts released a report concluding that the EPA's recent power plant directive, alongside anticipated measures limiting emissions of mercury and other toxic substances, would create hundreds of thousands of jobs.
The new bills are one consequence of the election last year that increased the size of the Republican contingent in both houses of Congress - a result that also killed any chance of passing legislation curbing emissions through the Senate.
But some Democrats - particularly those from coal states - also oppose EPA regulation, and analysts say it is as yet unclear whether the anti-regulation proposals command sufficient political support to ensure their passing.
If they do, President Obama may veto them.
However, continuing uncertainty over US plans is perhaps the single biggest obstacle to securing a new international deal under the UN climate convention; and the row between the EPA and its opponents adds further to doubts about the size of any potential US emission cuts.
"Unravelling EPA's authority to use national legislation to tackle climate change will be perceived by developing countries as yet one more example of the US 'do as what we say, not what we do'," one experienced observer with ties to several developing country delegations - who did not want to be named - told BBC News.
"And given extensive national legislation in developing countries that is already on the statute book or about to be, gives them serious cause to think whether the US is able to play any meaningful role in tackling climate change in the near future."