The nation's largest Internet service providers on Monday cautioned the Federal Communications Commission against any possible step that would land them more clearly under the agency's jurisdiction, posting that doing so could deter their investments in broadband networks.

A ruling against the agency is expected to hamper FCC Chairman Julius Genachowski's signature policy objectives, including open-Internet rules and the reform of an $8 billion rural telephone fund to extend broadband access in remote areas of the country.

However, some analysts feel that the agency would have to reclassify those services if it seeks to remain relevant as the Web becomes a primary vehicle for communication and entertainment.

"The proposed regulatory about-face would be untenable as a legal matter, and, at a minimum, would plunge the industry into years of litigation and regulatory chaos", the companies wrote.

The agency has said that its authority over ISPs derives from its supervision of other communications services, such as cable television.

Three judges grilled an FCC attorney during an oral hearing early last month; over whether that "ancillary authority" over broadband Internet services was suffice to rule against Comcast.