Verizon Wireless customers who have held on to unlimited data plans and use significantly more than 100GB a month will be disconnected from the network on August 31 unless they agree to move to limited data packages that require payment of overage fees.

Verizon stopped offering unlimited data to new smartphone customers in 2011, but some customers have been able to hang on to the old plans instead of switching to ones with monthly data limits. Verizon has tried to convert the holdouts by raising the price $20 a month and occasionally throttling heavy users but stopped that practice after net neutrality rules took effect. Now Verizon is implementing a formal policy for disconnecting the heaviest users.

The news was reported by Droid Life yesterday, and Verizon confirmed the changes to Ars this morning.

"Because our network is a shared resource and we need to ensure all customers have a great mobile experience with Verizon, we are notifying a very small group of customers on unlimited plans who use an extraordinary amount of data that they must move to one of the new Verizon Plans by August 31, 2016," a Verizon spokesperson told Ars. "These users are using data amounts well in excess of our largest plan size (100GB). While the Verizon Plan at 100GB is designed to be shared across multiple users, each line receiving notification to move to the new Verizon Plan is using well in excess of that on a single device."

The 100GB plan costs $450 a month.

Customers who don't switch plans by August 31 will get their lines shut down but can reactivate their accounts within 50 days by switching to a limited plan, Droid Life wrote.

About 99 percent of Verizon Wireless customers have plans with data limits. Those who still have unlimited data are paying month to month as their contracts likely expired.

Verizon's efforts to restrict grandfathered unlimited data customers have sometimes been controversial. In 2014, the company unveiled plans to throttle 4G LTE speeds at congested cell sites for customers who used 4.7GB or more of data per month. Federal Communications Commission Chairman Tom Wheeler demanded that Verizon justify the policy, saying it appeared to be an attempt to boost profits rather than perform necessary network management. Verizon resisted at first, saying unlimited data customers would otherwise "have no incentive to limit usage during times of unusually high demand."

Verizon eventually caved, saying it wouldn't start throttling 4G data but maintained its already existing policy of throttling heavy 3G users. The 3G throttling remained in effect until mid-2015. Verizon ended the throttling after the FCC issued new net neutrality rules, though the rules aren't clear on whether throttling in this type of situation is allowed under the "reasonable network management" exception. Other carriers including AT&T and T-Mobile USA still throttle the heaviest users of unlimited data when the network is congested without being challenged by the FCC.

While wireless data plans without monthly limits aren't as plentiful as they once were, T-Mobile and Sprint still make unlimited plans available to all new customers, while AT&T offers unlimited data if you also subscribe to the company's TV service.

AT&T has also tried to push customers off of its oldest unlimited data plans but has taken less drastic measures than Verizon. While Verizon raised its unlimited data price by $20, the AT&T price was raised for the first time in seven years last December and only by $5 a month.