Cox is now charging its customers $50 extra each month for unlimited data.

Cox also introduced a $30-per-month charge that adds 500GB to the standard 1TB data plan. Cox customers who go over the 1TB cap without having purchased extra or unlimited data pay a $10 charge for each additional 50GB. Naturally, "unused data does not roll over," Cox says.

DSLReports reported Monday that the new $50 and $30 fees would be rolled out this week, and Cox confirmed it with details on its website. There's also an FAQ. "Our additional data plans are flexible to meet our customers' changing needs—you can add or remove an additional data plan as needed and will see a prorated charge on your bill," Cox said.

Cox's data cap charges mostly follow the model of Comcast, which also charges $10 overage fees and $50 extra per month for unlimited data. Comcast does not offer the $30-for-500GB option, however.

Cox, the third-largest cable company in the US after Comcast and Charter, has about 6 million residential and business customers in 18 states. It has rolled the data caps out on a city-by-city basis, so not all Cox customers face the caps yet.

Last month, we noted that Cox brought the overage fees to Arizona, Louisiana, Nevada, and Oklahoma. Cox was already enforcing data caps and overage fees in Arkansas, Connecticut, Florida, Georgia, Idaho, Iowa, Kansas, Nebraska, and Ohio.

Listing image by Aurich Lawson | Getty Images