RTFA: http://www.yalerotc.org/Solomon.html

The 1996 Solomon Amendment provides for the Secretary of Defense to deny federal funding to institutions of higher learning if they prohibit or prevent ROTC or military recruitment on campus.

This law has been codified in 10 USC Sec. 983. Version in effect as of Jan 2000 shown here.

Apparently there have been some suggestions to deny federal funding for Columbia University based on this law.