Chief Justice John Roberts could decide on a motion to halt the Obama administration's far-reaching climate rules as soon as this week, say lawyers familiar with the litigation.

Two motions to stay Obama's climate rules were sent to the Supreme Court last week, one from 29 states and another by dozens of utilities, large manufacturers and oil companies.

The climate plan, called the Clean Power Plan, is unprecedented in scope, which is why so many groups and states oppose it. The plan directs states to reduce greenhouse gas emissions a third by 2030, as part of a broader administration effort to combat manmade climate change. Many scientists say the emissions, primarily carbon dioxide from the burning of fossil fuels, are causing the Earth's climate to warm, resulting in more severe weather, longer droughts and more flooding.

The request to halt the rules came less than a week after the D.C. Circuit Court of Appeals rejected a stay request by the states and industry. Yet the court did expedite oral arguments on the merits of the plaintiffs' separate lawsuits against the plan, which will move forward in June.

But that wasn't enough for the opponents of the landmark regulation, and they almost immediately asked the high court to consider staying the rule ahead of lower court's decision.

Such motions usually go directly to the chief justice, lawyers say. Roberts promptly responded by ordering the Environmental Protection Agency, the respondent in the case, to reply to the motions by Thursday.

"Nothing will happen before that," said one lawyer who did not want to be named.

The quickest scenario involves Roberts issuing the decision "right away by himself," in which case the petitioners "could get a decision as early as next Friday," the lawyer said.

But given the importance and complexity of the case, Roberts likely will want to circulate his decision to other justices to weigh in, which "could take several days."

Adding to that, the petitioners will have to respond to EPA's brief, but that could come quickly.

"We are asking at its core for injunctive relief ... to get the court to act quickly," said Ross Eisenberg, vice president for energy and regulatory affairs at the National Association of Manufacturers, one of the groups asking the high court for a stay. He said the groups are "expecting a quick turnaround."

A decision on halting the Clean Power Plan could happen, realistically, in the next two weeks, said Jeff Holmstead, former head of EPA's air office under former President George W. Bush and now a partner at the law firm Bracewell Giuliani.

"I imagine that the stay requests will be fully briefed by February 12th at the latest," he said in an email. "We could get a decision any time after that — perhaps the week of February 15th.

"Of course there's no deadline for the court to decide, so they may take a while longer, given the number of pages that have been filed," he said, noting that new motions were filed separately by North Dakota, a large shale oil producer. The same day Roberts' order was issued, "three more stay applications were submitted," along with the one from North Dakota on Friday. "So he may give them [EPA] a few more days to respond to those applications as well."

The stakes are high. If the Supreme Court issues a stay, it effectively places the centerpiece of Obama's climate change agenda on ice and ensures the EPA won't begin the first stage of implementation before he leaves office.

But Holmstead and other lawyers say that is a "long shot."

"The court has never granted a stay of an EPA rule after a stay was denied by a lower court," Holmstead said. "On the other hand, the [Clean Power Plan] is very different from any other rule EPA has ever issued, and the court will be aware that."

It brings to mind last year's Supreme Court case on the high cost of EPA's mercury and air pollution rules for coal plants, he said. In that case, the justices ruled in favor of states and business, but "its decision was essentially irrelevant because almost all plants were required to comply before the case was decided by the Supreme Court." He says the court may want to avoid a similar result.

The motions outline the urgency of halting the Clean Power Plan from taking effect due to the far-reaching economic harm it will cause.

The EPA requires states to create and submit compliance plans to slash their emissions beginning in September, setting in motion the first phase of the plan's emission reduction requirements. The plans will go into effect beginning in 2022, with state-by-state emission reductions required to be achieved by 2030.

The states argue that the plan is a federal "power grab" that goes far beyond the authority given to the agency by Congress under the Clean Air Act. Business groups say the plan poses a threat by raising costs, changing the nation's electricity fuel mix, and threatening the reliability of the power grid by increasing the likelihood of power outages.

Republican lawmakers oppose the Clean Power Plan as regulatory overreach that won't have any significant impact on lowering greenhouse gas emissions and slowing global warming.