Renewed Spotlight on Why the National Football League Is a Nonprofit Group

The NFL isn't the only sports group that's a nonprofit, but it's the richest.

The NFL league office has been a tax-exempt 501(c)6 trade association since the 1940s. The Professional Golfers Association and National Hockey League are also nonprofit trade organizations, though neither comes close to the wealth of the NFL.

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Though the potential taxes owed if these sports leagues were classified as a for-profit entity are estimated at a modest $10 million, the fact that the NFL league office is tax exempt at all is rubbing some people the wrong way anew because of the recent scandals, including the controversial player concussion issue.

The NFL contends that the league office is an administrative office that writes the rules of the game, hires referees, negotiates collective bargaining agreements and more.

A spokesman for the NFL offered to ABC News as comment an op-ed by Jeremy Spector, the NFL's outside tax counsel and partner with Covington and Burling LLP.

"The league office acts as a trade association for the NFL clubs," Spector wrote in November. "It establishes rules and standard practices for its members, develops programs to help them run their operations more efficiently and profitably, and promotes the business in the broader community. Trade associations are nonprofit organizations. They don’t engage in any business activity. As a result, they are exempt from being taxed under section 501(c)(6) of the federal tax code."

"Taxpayers are losing $10 million a year subsidizing these tax loopholes for professional sports leagues that generate billions of dollars annually in profits," Coburn told CNBC.

Goodell made a total of $85 million from 2010-2012, the last three years for which information is available. Though the other major sports leagues don't publish executive pay, Goodell is widely thought to be the highest-paid sports commissioner, according to industry experts.

The 2012 tax form shows more than $833 million in mortgages and notes to third parties, which the NFL told CNBC are loans for club members as part of the league's G-3 stadium fund. This fund helped clubs build new stadiums.