The latest imposition of NFL power over its players goes something like this:

If someone, anyone, makes a public allegation, substantiated or otherwise, recanted or supported, of possible improper conduct, the player must submit to an investigation on the league's terms or face suspension.

That's essentially what the NFL said Monday in a letter to the NFL Players Association as a final warning to four players named in an Al-Jazeera report on the use of performance-enhancing drugs.

The source for the report has since retracted his information, and the league already has cleared the name mentioned most prominently: retired quarterback Peyton Manning. But if the Green Bay Packers' Julius Peppers and Clay Matthews, the Pittsburgh Steelers' James Harrison and free agent Mike Neal don't play ball with the NFL -- if they don't step forward to prove their innocence, as it were -- then they will be suspended as of Aug. 26.

It would be easy to say that a rule-abiding player has nothing to worry about, but I'm going to guess that New England Patriots quarterback Tom Brady and retired defensive lineman Anthony Hargrove, among others, might not agree.

Packers linebacker Clay Matthews called the claims in the Al-Jazeera report "bogus" at the start of training camp. AP Photo/Morry Gash

As I said Monday night on SportsCenter, there has been -- to put it diplomatically -- plenty of gray area in previous NFL investigations. Based on recent history, at least, these players are more likely to be disciplined for their conduct during the investigation than for any of the allegations that spurred the investigation in the first place.

Brady will serve a four-game suspension to start this season because the NFL determined he was "more likely than not" involved in a scheme to deflate footballs in the 2014 AFC Championship Game. The league's final report, of course, carried not a shred of direct and verified evidence that Brady was involved -- or even that the balls themselves were artificially deflated. It focused heavily on Brady's refusal to provide his mobile phone, even though he said he provided all the information the league requested from it.

Hargrove, meanwhile, essentially lost his career in 2012 when the NFL pinned much of its Bountygate investigation on him telling his New Orleans Saints teammates to "pay me my money" after a hit on then-Minnesota Vikings quarterback Brett Favre. Hargrove adamantly denied saying it, and the NFL concluded he was not being truthful in his deposition. Later, an NFL Films video confirmed Hargrove's account. The NFL quietly acknowledged it.

The point, of course, is that Peppers, Matthews, Neal and Harrison have been smart in approaching the latest investigation with extreme caution. One wrong move, or one perceived to be uncooperative by the league, and they'll forever be stained by NFL discipline.

The NFL already has a PEDs policy, to which all four players have been subject. The policy's testing procedure should be the source of any allegation. Unless one or more of them have tested positive, they are innocent under the terms of the agreed NFL-NFLPA policy. The policy does allow for discipline if violations are found through "sufficient credible documented evidence," but unless the NFL has uncovered something more than Al-Jazeera did from a now-discredited source, it's difficult to imagine what that might be.

In this case, the NFL is asking the players to step outside the policy and answer to the allegation anyway. Ask Brady and Hargrove, both of whom denied their respective accusations from the start, how that worked out for them.

In truth, this really isn't about PEDs. Again, the NFL has a policy for that. This is another maneuver in the now-ubiquitous power struggle between the league and its players. The NFL is emboldened by its legal victory over Brady and is using the same broad authority -- as written in Article 46 of the collective bargaining agreement -- to compel participation in an otherwise out-of-policy investigation.

If you celebrated Brady's discipline, surely you realized that your team could be next. You did realize that, right?

At the moment, it's difficult to imagine the limits of the league's power. Even in a union environment, with a legal CBA in place, we might finally have reached the moment when players are subject to discipline whenever they don't do what the NFL asks of them. If you thought the relationship between the two sides was icy and too litigious already, wait until you see what's next.