Verizon customers who still have the old unlimited data plan may face a new $20 upcharge, but they will not be throttled.

Verizon recently announced customers who were grandfathered into the unlimited data plan would be subject to a $20 monthly charge. These customers can keep those plans and use as much data as they want without having their data speeds decreased (throttled) by Verizon, CNet reports.

Verizon's Chief Financial Officer Fran Shammo said in an interview Tuesday unlimited data users can use as much data as they want, and Verizon will not slow them down when they reach a certain amount.

Verizon is the only company of the major four carriers in the U.S. that does not throttle users when they reach a certain amount of data usage in a month. Just last week, Sprint said they would start throttling users when they reached a specific amount of data use each month.

Data is very expensive for wireless carriers, but Verizon refuses to restrict users access to their high speed data by throttling them to much slower speeds like their competitors do.

"For a customer who signed up for unlimited, they're going to get unlimited," Shammo said. "But we are increasing the price. These customers are consuming a lot of data. But we're not in the habit of throttling customers." 

Verizon discontinued unlimited data plans four years ago, but customers who left their plans alone were allowed to stay on the unlimited data plan. Verizon has tried to encourage these customers to change their plans by not offering phone discounts to them and adding the $20 upcharge.

Only about 1 percent of all Verizon customers remain on the old unlimited data plan. Others have switched over to plans that offer a set amount of data.