The NFL has said the four linebackers being investigated for an alleged link to performance-enhancing drugs will be suspended, if they don't agree to be interviewed by the league in the next 10 days.

NFL senior vice president of labor policy and league affairs Adolpho Birch sent a letter Monday to the NFL Players Association detailing the plan to suspend James Harrison of the Pittsburgh Steelers, Clay Matthews and Julius Peppers of the Green Bay Packers and free agent Mike Neal if they don't speak with the league by Aug. 25. Their punishment would then start the following day.

Birch's memo to the union was obtained by The Associated Press, according to a person with knowledge of the investigation who was not authorized to speak publicly about it.