The Legislative branch (The Congress) of the government is limited by the U.S Constitution, just as the two other branches are, through the system of check and balance. Through this system, all three branches of the government oversee, limit and check each other so no part abuse from its powers and a balance in the government exists. Through this principle, each branch can respond to the action of the other.
The legislative branch has the power to make laws, however, the President can veto those laws with a Presidential Veto, if this happens the legislative branch would still have a chance to override that veto with enough votes in both houses. The Judicial branch can also limit the Congress powers by using its power of declaring unconstitutional the laws that the Congress make.