T-Mobile has begun notifying customers that it’s hiking their rates by as much as $5 per line per month. The company’s help account on X confirmed the price increase, telling one person that it was “adjusting prices to respond to rising costs.” Reports suggest the hike applies to older plans, including One, Magenta, Magenta 55 Plus / Military, and Simple Choice, but the full extent isn’t known.

T-Mobile told employees that it is notifying the “small fraction of customers” who are affected by the change today, May 22nd, according to an internal document and slides published by The Mobile Report. The company added that the increases, which are either $2 or $5 depending on which plan customers are on, will show up on their next bill “as early as June 5th.”

T-Mobile made price lock-in promises in 2015, 2017, and 2022 for the plans that are reportedly affected. But notably, those promises didn’t cover every T-Mobile customer. The company excluded certain plans or limited them to customers switching plans or newly signing up. So it seems as though only those who fall outside of those terms are potentially seeing rate hikes. We’ve asked T-Mobile to clarify who might be affected.

Company consumer group president Jon Freier told employees that recent Go5G plans won’t be affected, nor will “millions of customers” under the company’s Price Lock guarantee, according to a memo seen by CNET.

Future rate increases could impact Price Lock-covered plans, though. T-Mobile revised the Price Lock promise this year so that, starting on January 18th, “customers activating or switching to an eligible rate plan” essentially have a get-out-of-jail-free card for leaving their contract early. If a price increase is too much, they can give the company 60 days’ notice, and it says it will waive their final month’s fees.