In a system of check and balance, the government has three different branches. All of them hold specific powers, and they all check each other. The three branches are: The legislative Power, which is the Congress. The Judicial Power which is represented by the Supreme Court. And lastly the Executive Power which is the President.
The President has the power of vetoing a law passed by the Congress. However, one way in which Congress can limit the President's power of executive appointment is by checking his/her decision with a 2/3 majority of the votes. This will override the veto done previously by the President.