WASHINGTON - More than 30 Democrats are asking tough questions about the government??s proposed voluntary guidelines for food marketing to children, Advertising Week reports. Led by Rep. John Barrow (D-GA), the group is sending a letter to the U.S. Department of Agriculture, U.S. Department of Health and Human Services and the Federal Trade Commission questioning the analysis behind the regulations. The letter also asks for a cost-benefit investigation of the guidelines.

In June, Rep. George Butterfield (D-NC) sent a letter to the agencies, and Sen. Mike Johanns (R-NE) is working on a similar one with other senators.

This interest in the proposal has come after months of intense lobbying by the food and beverage industries, as well as advertising and media firms, which all see the guidelines as expensive and harsh. But the voluntary nature of the rules has made fighting them hard.

The proposal??s voluntary nature "is one of the most controversial parts of this," said Dick O'Brien with the American Association of Advertising Agencies. "In years to come, if those standards stand, they will be used to measure the performance of the food and beverage industry."

While it can be difficult to rally forces against voluntary guidelines, the food and beverage companies have managed to garner congressional support. Butterfield??s letter read in part: "I am concerned that the IWG did not complete a study, as Congress directed, which considers the economic impacts of your proposal on broadcasters, advertisers, manufacturers, retailers, and charitable organizations. Although the IWG proposal would require considerable changes to food recipes and marketing, the IWG has produced no evidence that I am aware of that the proposed restrictions will serve the government's goals of changing long-term eating habits."