(a) Nothing in this Act is intended to contravene any existing treaty, law, agreement, or regulation of the United States. Contracts entered into in accordance with any treaty, law, agreement, or regulation of the United States shall not be in violation of this Act to the extent of that accordance. No preference shall be granted under this Act if that preference would contravene any treaty, law, agreement, or regulation of the United States.
     (b) The preference required by this Act is in addition to any other preference afforded by State law.