If they can levy taxes, they can raise a global bureacracy and a one-world army to impose its will...
Get the USA out of the UN and the UN out of the USA!
I feel the UN is the modern day League of Nations, and when it tries this, the first world democracies and republics that fund the UN will pull their funding and the UN will collapse under it's own corrupt and stupidity, much like the actual UN HQ building is doing right now in New York City.