USC has balked at giving permission to the New York Jets and Arizona Cardinals to interview Trojans offensive coordinator Kliff Kingsbury, league sources told ESPN.

Sources said a perfect storm of the NFL's new enforcement of an old rule has led to the situation where the Jets and Cardinals can't talk to one of their head-coaching candidates.

At last month's NFL owners meetings in Dallas, league officials informed team executives that they now had to request permission from college athletic directors to interview college coaches. Not doing so would be considered "conduct detrimental," and the NFL could then dock draft picks from teams, sources said.

"If permission is denied, the NFL club should respect that decision just as it would respect a similar decision from another NFL club," the rule states in part. "NFL clubs that fail to follow these protocols may be subject to disciplinary action for conduct detrimental to the League."

USC's refusal to release Kingsbury to interview has prevented the Jets and Cardinals from meeting with a candidate they would like to know more about. The teams have thus far moved on to interview other candidates while waiting to see if USC acquiesces.

Kingsbury was hired by USC as offensive coordinator and quarterbacks coach in December after being fired as Texas Tech coach after a 5-7 season. Kingsbury, 39, replaced Tee Martin, who was dismissed by coach Clay Helton in November.

He told ESPN's Shelley Smith in December that "I haven't even thought" about making the leap to the NFL and said he was looking forward to the impact he can have on college players. But sources previously told ESPN that before taking the USC job, Kingsbury had been pursued by multiple NFL franchises, and he clearly is continuing to draw interest at the pro level.

The NFL's new enforcement has made interviewing college coaches this offseason more challenging, certainly for teams that are interested in candidates such as Kingsbury.