Executive orders can be nullified by Congress but only with difficulty. Congress could adopt a law to overturn an executive order, but that law could be vetoed by the President. Congress could then seek to overturn the veto with two-thirds majority votes in the House and the Senate, as required by the Constitution. Historically, Congress has overridden only ten percent of all presidential vetoes. Congress can use another option: it can prevent funds from being used to implement an executive order.
Excepted from Trust and The Presidency, Part 5 of 7.