Broadband providers could still create Internet fast lanes even if federal regulators adopt stronger rules for the Web, as net neutrality advocates are hoping.

That's what the cable industry is arguing in a letter to the Federal Communications Commission. The letter, filed Wednesday by the National Cable and Telecommunications Association, opposes the labeling of broadband companies as utilities — a move that would give the FCC much greater authority over Internet service providers like Comcast and Verizon.

At issue is whether the FCC should regulate those firms like phone companies under Title II of the Communications Act, the law that serves as the commission's charter. The FCC's current proposal would regulate broadband companies under Title I, Section 706 — a part of the law with murkier implications.

"Subjecting broadband access providers to regulation under Title II would not even accomplish the goal that reclassification proponents apparently seek," the letter reads. "Reclassification would not support a categorical prohibition on Internet 'fast lanes' any more than Section 706 would."

The cable guys may have a point: A Title II approach would allow the FCC to ban all ISPs from speeding up or slowing down traffic, but only to a point. Under the law, Title II can only be used to ban "unreasonable" or "unjust" discrimination. If the broadband providers can successfully argue that creating an Internet fast lane falls within this loophole, then they would be free to set up a tiered Internet just like the one allowed by the current plan being considered by the FCC.

Even supporters of "strong" net neutrality acknowledge the loophole exists. "The first big problem with the 'unreasonable discrimination' approach is that it's utterly unworkable," wrote Chris Riley, Mozilla's senior policy engineer, in a blog post on net neutrality as far back as 2010, when the FCC was writing an earlier version of its net neutrality rules. "What does 'unreasonable discrimination' even mean? Is it 'reasonable' for a network operator to block BitTorrent or another peer-to-peer program, just because it sometimes uses a lot of bandwidth? That's in the eye of the beholder."

NCTA's letter comes a day after executives from top broadband companies wrote their own letter of opposition to FCC Chairman Tom Wheeler.

"Reclassification of broadband Internet access offerings as Title II – telecommunications services — would impose great costs, allowing unprecedented government micromanagement of all aspects of the Internet economy," the CEOs of Verizon, AT&T and Comcast wrote, along with 25 others.

Title II regulation would give the FCC much wider latitude to regulate broadband providers in general. But these two words — "unjust" and "unreasonable" — nevertheless pose a thorny problem for consumer advocates.

The full letter is below.