50 cal,
The UN does not need America's permission to go forward with its agenda. It can do whatever it wants. BUT to calm your nerves... Anything the UN does is not binding on the US unless it passes a 2/3 vote of the Senate.
The UN can pass a mandate that all governments must confiscate guns from their citizens. America would not have to abide by this unless 67 senators vote to ratify the UN mandate. Even if President Obama agrees to the mandate and signs the treaty, he cannot enforce it unless 2/3 of the Senate say he can.
This comes directly from the Constitution Article II, Section 2, Clause 2. "He [the president] shall have Power, by and with the Advice and Consent of the Senate, to make Treaties, provided two thirds of the Senators present concur."
The UN cannot take away our guns without our permission. Feel better?