Verizon on Thursday confirmed it is moving legacy unlimited subscribers who use an “extraordinary” amount of data on to its new plans by August 31.

The shift, first reported by Droid Life on Wednesday, will only apply to a “very small fraction” of Verizon’s customer base who use well in excess of 100 gigabytes of data each month on a single device, a Verizon spokeswoman said. Such usage is “highly unusual,” the spokeswoman said.

“These users are using data amounts well in excess of our largest plan size (100 GB),” Verizon’s spokeswoman said in an emailed statement. “While the Verizon Plan at 100 GB 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.”

Since the network is a shared and finite resource, the spokeswoman said Verizon is making the change to “ensure that our broader customer base has a great experience.”

The new Verizon plan these customers will be switching to – the carrier’s highest-tier, 100 GB plan – runs $450 per month, the spokeswoman said.

Customers impacted by the change will be notified both via a message on their monthly bill and a letter in the mail, the spokeswoman said.

Verizon officially ended its unlimited plans in July 2011, but it seems a handful of legacy users have managed to hang on.

Verizon’s spokeswoman said the carrier is not looking to disconnect anyone, but said users who fail to make the change by the August 31 deadline could face an interruption of service.