This Act of Congress is sometimes known as Section 3679 of the Revised Statutes, as amended.
To some extent, but not entirely, it implements the provisions of Article I, Section 9, Clause 7 (the "power of the purse") of the Constitution of the United States which precludes the expenditure of funds by any branch of the Federal government unless those funds have been appropriated by Congress. In part, the Act is actually inconsistent with the Constitution because it recites that expenditures without appropriations can be made where expressly permitted by Congress: the Constitution permits no such exception.
Although the ADA and its predecessors are over 120 years old, no one has ever been convicted or even indicted for its violation.. (Emphasis mine...may Obama be the first to be convicted. ~ Storm'n Norm'n)