Factories, refineries, and power plants may be able to combine emissions increases from separate—yet related—projects for permitting purposes under an EPA regulation now under review at the White House Office of Management and Budget.

White House regulatory reviewers began their evaluation July 6 of a rule that could revive a January 2009 Clean Air Act permitting regulation issued by the departing George W. Bush administration. The Obama EPA then halted the regulation in response to a reconsideration request by...