Siding with Verizon, the National Advertising Division of the Better Business Bureau recommended that Comcast should stop advertising Xfinity as the fastest broadband service in the country.
Verizon had complained to the NAD that Comcast misled consumers by running ads with copy like "the fastest downloads available" and "It's official. We're the fastest."
Those ads referred to a PC Magazine study conducted last year, which found that Comcast offered nationwide average download speeds of 18.64 Mbps compared to Verizon's nationwide average download speed of 16.20 Mbps.
But Verizon contended that the study didn't accurately reflect the differences in speed between its FiOS network -- which offers downloads of up to 150 Mbps, but isn't available in much of the country -- and the far slower DSL network. Verizon said the study should have treated FiOS and DSL as two separate broadband providers.
The NAD said in its decision that PC Magazine actually ranked three ISPs -- Comcast, Cox and Charter Communications -- as fastest. Of those, Comcast has the fastest download speeds, but Cox has the fastest uploads.
The NAD recommended that Comcast can "communicate that it is one of the fastest ISPs in the nation according to PC Magazine or the fastest Internet option for most consumers in its footprint where FiOS is not available."
While Verizon and Comcast were adversaries in the NAD proceeding, the companies recently said they intend to work together.
Verizon recently said it plans to pay almost $4 billion to license spectrum from four cable companies. The agreement also provides for Verizon and the cable companies to market each other's services.
Verizon and Comcast are already co-marketing their services in Seattle, Portland and the San Francisco area. The companies are offering a quadruple-play deal that allows consumers who sign up for Comcast's Xfinity TV bundle and Verizon's mobile phone service to receive a $300 prepaid Visa debit card.
Consumer advocates have cricized the cross-marketing deal, arguing that it will prove anti-competitive. This week, six Democratic House members asked the FCC and Justice Department to closely scrutinize the proposed deal.