Sen. Russ Feingold is growing concerned about radio's enforcement of anti-payola policies agreed to in the FCC consent decree in April, and wants to know what the four biggest broadcast groups are doing to enforce the rules.

In a particularly pointed, two-page letter sent Wednesday to CBS Radio's Dan Mason, Citadel's Farid Suleman, Clear Channel's Lowry Mays and Entercom's David Field, the Wisconsin Democrat referred to the eight "Rules of Engagement" the companies agreed to in April, which laid out how the radio giants would ensure fair interactions with labels, artists and their representatives. Feingold now wants evidence the companies have been abiding by the new rules.

"Now that you have had a couple months to put this rule into place, I'd like to request more information on what access you have provided and how it has been publicized. Have you taken any efforts to increase the amount of access provided and to facilitate submissions?" Feingold writes in the letter. "I'd also be interested in knowing whether this access is through each individual station, to the corporate playlists and testing pools, if applicable, or both."

Feingold reminds the group executives that the second rule of engagement states: "Radio should not be allowed to sell or barter access to its music programmers" and that he is "concerned by recent reports that some Clear Channel stations are requiring the grant of a royalty-free right and license to the music upon submission. As the debate surrounding the recent Copyright Royalty Board decision to increase the royalty rate for digital performances indicates, these rights clearly have value." He says the required royalty waiver seems to violate the April commitment not to barter access to music programmers. "I encourage you all, and Clear Channel in particular, to clarify this issue."

In what is clearly a threat to introduce tough legislation on payola if he doesn't get a satisfactory response from broadcasters, Feingold says, "It is very troubling that the voluntary rules seem to have been violated after just a few months…I hope that your commitment to meaningful rules of engagement and efforts to eliminate the pervasive payola documented by then-New York Attorney General Spitzer remains strong and look forward to your response."

Radio & Records, Billboard.biz sister publication, reached out to all four companies involved and provided them a copy of Feingold's letter. CBS Radio said it had not yet received Sen. Feingold's letter directly from his office, but that it will respond appropriately when it does. A CBS spokeswoman also pointed out that since it agreed to recognize the Rules of Engagement, its stations have presented music in the manner outlined in the airtime commitment, featuring independent artists and specialty programs in major markets across the country.

Citadel, Clear Channel and Entercom did not respond to R&R's query.

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