I don't see one if the standard legal test, first described by Supreme Court Justice Robert Jackson, who said the president's authority to issue executive orders is strongest when he does so with the backing of Congress (category one), more dubious when he issues an order pertaining to a topic on which Congress has not passed a law (category two), and weakest when the executive order is "incompatible with a congressional command" (category three) delaying the employer mandate is clearly in category three. I cannot say whether the president has the authority to set the pay scale for people that contract with the federal government.

And yet, they roll on.