There is no Constitutional provision or statute that explicitly permits executive orders, there is a vague grant of "executive power" given in Article II, Section 1 of the Constitution and the statement "take Care that the Laws be faithfully executed" in Article II, Section 3.
Until the 1950s, there were no rules or guidelines outlining what the president could or could not do through an executive order. However, the Supreme Court ruled in Youngstown Sheet & Tube Co. v. Sawyer, 343 US 579 (1952) that Executive Order 10340 from President Harry S. Truman placing all steel mills in the country under federal control was invalid because it attempted to make law, rather than clarify or act to further a law put forth by the Congress or the Constitution. Presidents since this decision have generally been careful to cite which specific laws they are acting under when issuing new executive orders.
To date, U.S. courts have overturned only two executive orders: the aforementioned Truman order, and a 1996 order issued by President Clinton that attempted to prevent the US government from contracting with organizations that had strike-breakers on the payroll. Congress may overturn an executive order by passing legislation in conflict with it or by refusing to approve funding to enforce it. In the former, the president retains the power to veto such a decision; however, the Congress may override a veto with a two-thirds majority to end an executive order.
Executive orders as issued by state governors are not laws, but do have the same binding nature.