An Act of Congress is a bill or resolution adopted by both houses of the United States Congress to which one of the following events has happened:

1. Acceptance by the President of the United States,
2. Inaction by the President after ten days from reception (excluding Sundays) while the Congress is in session, or
3. Reconsideration by the Congress after a Presidential veto during its session.

The President promulgates Acts of Congress made by the first two methods. If an act is made by the third method, the presiding officer of the house which last reconsidered the act promulgates it [1] (http://www4.law.cornell.edu/uscode/1/106a.html).

Under the United States Constitution, if the President does not return a bill or resolution to Congress with objections before the time limit expires, then the bill automatically becomes an act; however, if the Congress is adjourned at the end of this period, then the bill dies and cannot be reconsidered (see pocket veto). In addition, if the President rejects a bill/resolution while the Congress is in session, a two-thirds vote of both houses of the Congress is needed for reconsideration to be successful.

Congress's powers are fairly broad, but no Act of Congress may violate the Constitution, nor otherwise exceed the powers granted to Congress by the Constitution, and if found to do so by the Supreme Court will be struck down.