The UN wants to make all private ownership and possession of firearms illegal. Therefore any sale or trade of firearms to or by any private party would be "illicit" and punishable by the UN. The US has to make it clear to the UN gun grabbers that we will not agree to or tolerate any such negation of our Constitutional rights by any outside organization.
This is just one more excellent reason why the US has no business being part of the UN. The socio-political philosophy and agenda of the vast majority of UN nations is diametrically opposed to that of the US. I want the US out of the UN and the UN and it's arrogant, corrupt, lawbreaking agents of 2-bit totalitarian regimes out of the US.
They're not violating you Second Amendment rights, they're just "regulating commerce". The New Deal writ large.