Article 1, Section 9 of the US Constitution states:
"No Money shall be drawn from the Treasury, but in Consequence of Appropriations made by Law; and a regular Statement and Account of the Receipts and Expenditures of all public Money shall be published from time to time."
Meanwhile, congress and the president have their pay protected.
president: Article II, Section 1 - "The President shall, at stated Times, receive for his Services, a Compensation, which shall neither be increased nor diminished during the Period for which he shall have been elected..."
congress: Amendment XXVII - "No law, varying the compensation for the services of the Senators and Representatives, shall take effect, until an election of representatives shall have intervened."
Nothing states their amount of pay.