The Federal Communications Commission (FCC) is fining AT&T $100 million for misleading customers about its unlimited data plans, the agency announced Wednesday. The telco slowed down unlimited data plans, and didn’t inform consumers about such throttling, according to the FCC. “Unlimited means unlimited,” said the FCC’s enforcement bureau chief Travis LeBlanc. “As today’s action demonstrates, the commission is committed to holding accountable those broadband providers who fail to be fully transparent about data limits.”

AT&T said Wednesday that it is going to “vigorously dispute the FCC’s assertions” and that it has been adequately informing customers about the practice in question.

AT&T introduced a so-called maximum bitrate policy in 2011, effectively slowing down the connections of customers with unlimited data plans after they had surpassed a certain amount of data for any given month. This violated the FCC’s existing net neutrality rules, according to the agency, and made it hard for affected customers to use apps or browse the Web on their phone.

A lot of that usage is these days driven by video viewing: 45% of all mobile data traffic is now video-related, according to data from Ericsson, which estimated in a recent report that video will make up 60% of all mobile data by 2020.