All four major service providers in the U.S. have been accused of violating the last remaining net neutrality rule, a day after President Barack Obama said he was against the Federal Communication Commission’s proposal to institute controversial internet “fast lanes” that would further threaten equality for web-based companies.

T-Mobile, Sprint, AT&T, and Verizon have all been accused of violating the transparency rule left in place to help safeguard net neutrality after a federal appeals court ruling knocked down several anti-discrimination and anti-blocking regulations.

The transparency requirement was upheld to ensure that carriers disclose their information about network performance and management policies, but consumer watchdog group Public Knowledge on Wednesday sent letters to the companies accusing them of shrouding their throttling plans in secrecy and demanding that they disclose or suspend the practices.

Throttling is the intentional slowing down or limiting of customers’ internet service by a provider — a controversial practice that has ended in court for cable companies like Comcast.

“Sprint and Verizon violate the transparency rule by failing to meaningfully disclose which subscribers will be eligible for throttling,” Public Knowledge wrote. “AT&T, Sprint, and Verizon violate the transparency rule by failing to disclose which areas of the network are congested, thus subject to throttling. T-Mobile violates the transparency rule by preventing throttled subscribers from determining the actual network speed available to them.”

The letters come as the FCC continues a long-standing debate over whether to abolish net neutrality entirely and instead establish a discriminatory “paid prioritization” model that would create fast and slow internet lanes, allowing wealthy companies to simply pay ISPs for speedier services, while those without as much capital would be forced to contend with sluggish or unreliable connections and loading times. The model was introduced by FCC chairman Tom Wheeler, a former lobbyist for the cable and wireless industries. While supporters say the proposal would not lead to “commercially unreasonable” arrangements with big companies, numerous advocacy and internet freedom organizations have opposed and disputed it, noting that it would risk development opportunities for new startups and allow providers to charge customers more for services.

At the US Africa Leaders Summit on Wednesday, Obama voiced his disagreement with the FCC proposal, saying, “you don’t want to start getting a differentiation in how accessible the Internet is to different users. You want to leave it open so the next Google and the next Facebook can succeed.”

Craig Aaron, president of internet watchdog group Free Press, said the FCC’s plan “would encourage individualized negotiations and allow new kinds of discrimination. It would strand the next Google or Facebook in the slow lane.”

In addition to sending letters, Public Knowledge will also file a formal complaint with the FCC against the four carriers. However, Wheeler’s anti-net neutrality stance conflicts significantly with the consumer advocacy group’s demands; as the former president and CEO of the Cellular Telecom and Internet Association, Wheeler spent 14 years lobbying for AT&T and Verizon’s interests.

In July, Wheeler criticized Verizon for throttling plans of subscribers who had paid for unlimited data. However, when he asked the company to justify its policy, Verizon explained that capping unlimited plans was entirely legal and acted as an “incentive” to stop customers from using their phones too much.

Verizon also defended its practice by telling the FCC that all major carriers throttle their customers’ service plans. “This practice has been widely accepted with little or no controversy,” said Kathleen Grillo, Verizon’s senior vice president of Federal Regulatory Affairs. “The network’s capacity remains a shared and limited resource that we must manage to provide the best experience for all of our consumers.”

Michael Weinberg, vice president at Public Knowledge, said, “If the FCC’s transparency rules mean anything, they must require carriers to let subscribers know why, when, and to what speed their connections might be throttled. Today, Sprint and Verizon subscribers will not know if they are eligible for throttling until after they have crossed the usage threshold. AT&T, Sprint, and Verizon subscribers will not know they will be throttled until they are actually connected to a congested cell site. T-Mobile subscribers do not know the actual speed of their throttled connection. This is far from transparent.”

Weinberg said that if the companies did not disclose or suspend their throttling policies, that the FCC should “move quickly to resolve these violations of its rules.”

There has been no response yet from the FCC to Verizon over its previous throttling charges.

This article was originally published on Common Dreams.