U.S. to Push for New Economic World Order at G20

http://www.reuters.com/article/topNews/idUSTRE58G34Z20090921?sp=true

The United States envisages the IMF playing a central role in a process of "mutual assessment" by making policy recommendations to the G20 every six months. ''

Where exactly in the Constitution does it say that deferring to extrenal bodies is acceptable?