Republicans and industry officials on Tuesday contended the Obama administration's climate pledge heading into global negotiations was on "very shaky legal ground"

"The reason the administration is on such shaky legal ground is they are attempting to achieve their goals through regulation and administrative fiat," Mandy Gunasekara, GOP counsel on the Senate Environment and Public Works Committee said at a Washington event assembled for diplomats whose nations will be participating at the United Nations-hosted talks later this year. Referring to a sweeping cap-and-trade bill that passed the House in 2009 but later collapsed in the Senate, she said, "Congress already disapproved this approach."

The event expanded on business and GOP efforts to undermine confidence in President Obama's commitments to the Paris climate talks set to begin in late November. Skeptics of the deal have warned other nations that the centerpiece of the president's climate agenda — a rule limiting carbon emissions from power plants expected to be finalized this summer — eventually will have to clear the Supreme Court, and that Republicans don't support the rule or the climate talks.

But while opponents sowed doubt about the power plant rule's legal prospects and whether the Obama administration could even live up to the cuts it told the U.N. it could achieve, they said there's not much Congress can do to block the White House from agreeing to a deal in Paris.

"From my perspective, I'm not so sure there's all that much they can do," Stephen Eule, vice president for climate and technology with the U.S. Chamber of Commerce's Institute for 21st Century Energy, said Tuesday at the event, hosted by the American Council for Capital Formation, a free-market group.

Countries will meet in Paris in hopes of striking a global framework to govern emissions reductions beyond 2020. The idea is to prevent global temperatures from rising 2 degrees Celsius above preindustrial levels by 2100, though most experts are doubtful that enough political will exists to stomach the deep cuts needed to stay below that mark.

"A Paris agreement of some sort will be achieved," said Harlan Watson, the climate negotiator for former President George W. Bush. But whether it achieves the 2-degree goal "remains to be seen."

The White House has floated the idea that it can use existing treaties and non-binding pledges to cut emissions to avoid submitting a plan for a Senate ratification vote. It contends that treaties already on the books could be used to establish a binding system of formal reviews to ensure nations are making progress on reaching their emissions targets. Most climate scientists say that emissions of greenhouse gases, through burning fossil fuels, are driving manmade climate change.

Gunasekara said Republicans plan to pick apart the deal once it is finalized. She said Congress has a constitutional responsibility to weigh in if it believes the agreement is in the form of a treaty. Gunasekara said that such discussions are a "significant" part of the still-developing strategy to undercut the pact, and she made the case that cementing a binding system for reviews seemed like a formal treaty.

Regardless, the speakers said a significant gap exists between regulatory actions on the books and the 26 percent emissions cut Obama told the U.N. the United States would achieve by 2025. The Chamber contends that current actions would leave the U.S. about one-third short of that goal.

"Where is the administration going to get those extra tons [of emissions reductions]? Frankly, we don't know," Eule said.

Dave Banks, a former Senate Republican aide who now is executive vice president at the American Council for Capital Formation, surmised that additional emissions cuts could come from the industrial and agricultural sectors.

Such curbs would be opposed in rural America and among conservatives, Banks argued. That's key, Banks said, because while Obama could potentially sign a climate deal without congressional approval, the president's successor could back out of the agreement if achieving it becomes too difficult.

"The Congress can't stop the White House from signing an agreement ... but you have to have the stars and the planets line up on the legal side, the economic side and the political side," Banks said.

Obama will want to know more about the legal status of the power plant rule, which is sure to face a legal challenge, when he heads to Paris later this year. While the final outcome will be in doubt at that point, federal courts could try to give it an expedited review given that states are expected to file their plans for complying with the regulation one year after it's finalized, said Roger Martella, partner and co-lead of the environmental practice at Sidley Austin.

"There is a question of how soon will the courts look at this," Martella said.