AT&T plans to implement a new 150GB monthly usage cap for all DSL customers and a new 250 GB cap on all U-Verse users starting on May 2. AT&T on Monday said it will start charging extra after subscribers go past 150 gigabytes in a month, an amount it said only 2 percent of subscribers reach.

However, only users who exceed the new usage cap three times -- across the life of your account-- will be forced to pay these new per byte overages. Overages will be $10 for every 50GB over the 150 GB or 250GB limit they travel.

From March 18 to March 31, AT&T users are going to be receiving notices informing them of the change in the company's terms of service.

AT&T portrayed Monday's announcement as an attempt to curb "data hogs," but it could help the company preserve a revenue stream in the long run as people shift to Internet-based TV services.

Most U.S. Internet service providers already place limits on data traffic, but most of them don't charge extra when the limits are exceeded.