Provisions that were intended to sweeten the U.S. Environmental Protec­tion Agency’s newly proposed carbon emissions rule for industry are also what make it legally vulnerable, lawyers say. And they are likely to form the bedrock of a challenge.

“There’s a 100 percent likelihood it will be litigated,” says Roger Martella Jr., a partner in the environmental group at Sidley Austin who previously served as general counsel of the EPA. “This is likely to be the single most controversial rule from the EPA during the Obama administration.”