The NFL has sent all 32 teams a memo warning that they are subject to fines if they supply players -- knowingly or not -- with banned supplements.

The memo mentioned that a team already has been disciplined, without saying which team.

ESPN's Chris Mortensen reports that sources have told him the team was the Oakland Raiders, and the discipline came in the form of an undisclosed fine. The Raiders declined to make a comment.

NFL spokesman Greg Aiello confirmed that the memo had been sent, but he would not comment on which team already was disciplined.

Aiello said the memo to the teams emphasized that players are ultimately responsible for what they take, even if those substances are supplied by the team. However, the teams will be fined if they are found to be involved.

Last week, Carolina rookie Julius Peppers, who leads the NFL with 10 sacks, was suspended for four games after testing positive for a banned substance in a dietary supplement.

Peppers is appealing the suspension, which was announced by his agent, Marvin Demoff. The NFL has yet to confirm Peppers' suspension. He was in the lineup Sunday when the Panthers played Tampa Bay.

Another Panthers defensive lineman, Brentson Buckner, was suspended Nov. 4 for four games for violating the league's anti-drug policy. George Mavrikes, Buckner's agent, said his client took a dietary substance in training camp to help him lose weight.

It contained one of the substances now banned by the league.

Last spring, the NFL became the first U.S. sports league to ban ephedrine, a substance that also often is found in strength-building food supplements and can cause seizures, strokes or even death. It was done with the backing of the NFL Players Association.