WASHINGTON (MEDIA GENERAL) – The Federal Communications Commission levied a $100 million fine Wednesday against AT&T for intentionally slowing down Internet speeds for customers who had signed up for “unlimited” data plans.

The commission alleges AT&T “throttles” speeds for unlimited data customers once they use a certain amount of data, which it claims is a breach of transparency in selling unlimited data plans.

According to the Washington Post, the fine is one of the largest ever handed down by the FCC.

FCC Chairman Tom Wheeler said AT&T, the country’s second-largest mobile phone service, violated the commission’s rules on corporate transparency.

“Consumers deserve to get what they pay for,” Wheeler said in a statement. “Broadband providers must be upfront and transparent about the services they provide. The FCC will not stand idly by while customers are deceived by misleading marketing materials and insufficient disclosure.”

AT&T is familiar with throttling: The Federal Trade Commission sued the company in October, accusing AT&T of intentionally slowing Internet speeds. The FTC lawsuit claims 3.5 million users had data services slowed to “dial-up speeds” an average of 12 days per month, according to the Washington Post.