Net neutrality advocates demand action.

Representatives from Fight the Future, the Center for Media Justice and Free Press on Friday hand-delivered a 6-foot tall package containing 100,000 letters of complaint to the Federal Communications Commission. They ask the agency to take action against AT&T, Comcast, T-Mobile and Verizon for violating the agency's Open Internet order by offering so-called zero-rating service plans.

Zero-rating is a practice in which wireless and broadband providers exempt certain applications or services from monthly data caps. T-Mobile's Binge On service, which allows customers to stream unlimited video from certain services, is one example. Verizon's FreeBee program allows content owners to pay for a customer's data usage while using their service.

While the practice offers some benefits to customers, critics say it violates the agency's Net neutrality principles, which requires all services on the internet be treated the same. They claim it puts smaller competitors at a disadvantage and highlights the fact that data caps are unnecessary. Carriers say they are simply experimenting with new business models that will make their service more affordable for consumers.

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"These schemes are as much a problem for the internet as fast lanes," said Holmes Wilson, cofounder of Fight for the Future. "And that's why we're asking the FCC to enforce the rules, because these plans clearly violate net neutrality."

The FCC's net neutrality rules, adopted in February 2015 and upheld earlier this month by a federal appeals court, don't explicitly ban such deals. Instead, they allow the agency to review complaints individually. FCC Chairman Tom Wheeler initially praised T-Mobile's BingeOn service as innovative. But after net neutrality supporters expressed concern over the plans, the agency sent letters to several service providers, including AT&T, Comcast and T-Mobile, asking each company for details about its specific programs. The FCC has said it's met with each of the companies privately, but hasn't talked about the specifics from those discussions.

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Meanwhile, wireless and broadband companies say millions of consumers are benefitting from their "free data options."

"It's really discouraging to see these groups representing the digital elite put their own slanted views ahead of what's best for American consumers, particularly those living paycheck to paycheck," said Allison Remsen, executive director for Mobile Future, a group that counts AT&T and Verizon as members. "The idea that consumers would be better off if they were charged for something that mobile providers want to give them for free is preposterous."

But Free Press's Matt Wood said that's just the point. Customers are not really getting anything for free under zero-rated plans.

"We see data caps as the problem and zero rating as a symptom," he said. "What we want and need the FCC to do is ask questions about the carriers' plans that are already on the table, looking for any punitive and abusive practices, rather than simply taking ISPs at their word that caps are really reasonable and zero-rated data is really free."