When the announcement was made that the American Football League would merge with the NFL on June 8, 1966, the 16-team NFL needed to balance itself with the AFL by sending three NFL franchises to the newly formed 10-team American League Conference. At a special owners meeting in 1969, Commissioner Pete Rozelle locked the doors and told owners in attendance that nobody would be allowed to leave until three teams agreed to move to the new conference.
It was determined that certain NFC clubs would be exempt from going to the AFC because of geographical reasons. So, the New York Giants were safe because of the New York Jets, the Cowboys with the Houston Oilers, and the San Francisco 49ers were excused because of the cross-bay Raiders.