a constitutional right to reject a decision or proposal made by a lawmaking body."neither state was given a veto over amendments to the Act”.
It's an absolute power of a member to block any proposal or resolution single handedly in an organisation.
I assume you are talking about United Nations Security Council. It has five permanent members apart from 10 temperory members,who get terms on rotation basis. The permanent got their position by virtue of they being nuclear powers. The permanent members have veto power. Any single permanent member can block any resolution in the council.The permanent members are:
1.USA
- Great Britain
3.France
4.Russia
- China