WASHINGTON, DC — AT&T believes internet service providers are justified in blocking transmissions or choking the bandwidth of users who employ peer-to-peer software to trade files on the Web, according to a letter an AT&T vice president submitted to the U.S. Federal Trade Commission July 25th.“AT&T does not use network management tools to block the use of P2P applications by its mobile wireless broadband customers,” Robert Quinn, AT&T’s VP for federal regulatory issues, wrote in the letter addressed to FCC Commissioner Robert McDowell. “However, AT&T’s terms of service for mobile wireless broadband customers prohibit all uses that may cause extreme network capacity issues and explicitly identify P2P file-sharing applications as such a use. Under these terms of service, which are similar to those of other wireless providers, use of a P2P file-sharing application would constitute a material breach of contract for which the user’s service could be terminated.”

Quinn added AT&T hasn’t booted any of its broadband customers for using P2P applications, and he doesn’t believe any customers have used such software because of the nature of wireless broadband.

Observers of the wrangling between the FCC and Comcast Corp. over the latter’s interference with customers’ bandwidth in the name of network management have said they believe McDowell may use the letter to support a vote against sanctioning Comcast for the behavior.

The FCC is expected to vote Friday on the final disposition of its investigation into Comcast’s network-management practices. Earlier this week three of five commissioners — two Democrats and FCC Chairman Kevin Martin, a Republican — signed off on an order sanctioning Comcast for intentionally slowing or blocking the traffic of customers who used large amounts of bandwidth to transfer files via applications like BitTorrent. McDowell, a Republican, indicated he would vote against the majority.

Commissioners are not expected to fine the second-largest ISP in the U.S.