Just over two weeks ago, the FCC not-so-gently reminded all four big wireless carriers that although true “net neutrality” might not apply to them, there are still rules about transparency and disclosures that they have to follow. At the time, FCC chairman Tom Wheeler said that companies had no excuse to think the FCC wasn’t watching them — and the FCC isn’t the only group putting wireless companies on notice over their lack of transparency.

The consumer advocacy group Public Knowledge this week sent letters to Sprint, T-Mobile, AT&T, and Verizon, accusing them of violating the open internet transparency rule.

That rule doesn’t prevent a wireless carrier from, say, throttling their users’ service, but it does require them to be very clear about their plans to. Specifically, companies that provide broadband services, including mobile broadband, must “publicly disclose accurate information regarding the network management practices, performance, and commercial terms of its broadband Internet access services.” And they can’t just bury it in tiny fine print on an abandoned web site nobody can access with a sign saying “beware of the leopard.” The disclosure must be “sufficient for consumers to make informed choices regarding use of such services.”

The letters describe the three key ways in the four wireless carriers are violating this rule. Public Knowledge says that Sprint and Verizon fail to adequately disclose which consumers might face throttling, and that they and AT&T all fail to disclose which areas of the network are congested and therefore subject to throttling.

Although the companies do share some information, it’s basically useless to consumers and that violates the rule, the organization says. For example, Verizon openly admits that they throttle the data usage of their top 5% heaviest users, but that’s a moving target. Consumers have no way of knowing if their data usage is significantly higher than their neighbors’ until Verizon cuts them off.

T-Mobile, Public Knowledge says, violates the rule in a slightly different way: their network speed test apps are exempt from throttling, so subscribers whose service has been cut back can’t actually determine the real network speed they have available.

Sending a letter might not sound like a big deal, but it’s actually the first step in a formal legal process. Ten days after the wireless carriers get their letters, Public Knowledge can file formal complaints with the FCC about the companies’ actions.

The full text of all four letters is available on the Public Knowledge site.

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