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The NFL is not backing down on its insistence that the players named in an Al Jazeera documentary about performance-enhancing drugs must agree to interviews as part of the league’s investigation.

The players involved are Packers linebackers Julius Peppers and Clay Matthews, Steelers linebacker James Harrison and free agent (and former Packer) Mike Neal. Peyton Manning is also part of the NFL’s investigation, although his retirement means he’s no longer a member of the NFL Players Association and not a part of the ongoing battle between the league and the union over whether players must give interviews to league investigators.

The four players submitted affidavits responding to the allegations made against them in the Al Jazeera documentary, but Adam Schefter of ESPN reports that the NFL still insists that affidavits aren’t good enough, and they must give interviews.

The players’ union insists that the NFL has no right to investigate players unless there’s “credible evidence” that they used PEDs. The NFL says the league only needs credible evidence to impose discipline, not to launch an investigation. The league plans to send investigators to Packers camp and Steelers camp to interview the players, but the players are expected to decline to be interviewed.