The country's second largest wireless communications carrier is being fined $100 million for allegedly misleading customers over data plans that it said were "unlimited."

The move by the Federal Communications Commission, which is being fought by AT&T, follows a lawsuit filed against the company by the Federal Trade Commission, which alleged in October that the company had slowed Internet speeds for its customers.

According to a report by MetroSource, AT&T has said that it is common practice to "severely slow down speeds when a customer reaches a data threshhold in a given month."

Such actions by AT&T would violate net neutrality rules  by "throttling," or slowing Internet speeds on mobile phones.