I'd be more concerned with signing statements.

In one frequently used phrase, George W. Bush has routinely asserted that he will not act contrary to the constitutional provisions that direct the president to “supervise the unitary executive branch.” This formulation can be found first in a signing statement of Ronald Reagan, and it was repeated several times by George H. W. Bush. Basically, Bush asserts that Congress cannot pass a law that undercuts the constitutionally granted authorities of the President.

I would assume the Supreme Court would decided that.

EDIT: Site