NEW YORK (AP) - The NFL has told its teams to adhere to rules against tampering as a new three-day window for negotiating with free agents opened Saturday. Teams could contact representatives of free agents from other teams beginning at midnight, but the players can't visit any facilities or even talk to those clubs. The league has warned the teams against entering into any agreements with those players before free agency official kicks off on Tuesday at 4 p.m. Traditionally, contracts with free agents have been announced almost as soon as the NFL's business year begins, clearly indicating agreements had been reached before the free agency period began. The league has hoped to limit hints of tampering by creating the negotiating window.