A recently enacted NFL policy, which precludes players from endorsing companies that either manufacture or market products that contain substances banned by the league, has claimed its first victim.

Buffalo Bills wide receiver Eric Moulds has voluntarily ended his endorsement agreement with the Canadian-based company MuscleTech Research and Development after an investigation by league officials determined it violated the new policy.

"It was just easier to stop (the endorsement deal)," said Moulds' agent, Harry Henderson. "Rules are rules and this has become, essentially, a condition of employment. So, really, a player doesn't have any choice."

It is not known how much Moulds was paid for his endorsement.

The veteran wide receiver endorsed an all-natural protein supplement known as NITRO-Tech. In advertisements, many of which were posted on Web sites, Moulds claimed to have increased his muscle size and also his weightlifting capacity shortly after he began using NITRO-Tech.

While the product does not contain any substances on the NFL's banned list, MuscleTech does manufacturer products that contain ingredients not permitted by the league, such as ephedra and Androstendiol. The latter is an anabolic steroid. The NFL will begin testing for ephedra on July 1.

Moulds was unaware of the new policy, actually enacted last fall but suddenly getting more exposure because of the recent ephedra ban, and said he understands the rationale behind it. He said he specifically avoided endorsing products containing ephedra and did not realize the scope of the policy.

The investigation of Moulds' actions amplifies the claim recently made by NFL Players Association executive director Gene Upshaw that the policy will be strictly enforced and will not allow for ambiguity.

"It doesn't make sense for us to ban substances and then have players out there endorsing the companies that make the stuff," Upshaw told ESPN.com recently. "It doesn't send the right message. In fact, it's contradictory, we feel. We had to do something and we feel we are doing the right thing."

Upshaw said players have been apprised several times of the potential consequences if they violate the policy.

Len Pasquarelli is a senior writer for ESPN.com.