A consumer protection group in China is asking Apple to investigate problems with iPhone 6 and iPhone 6s units automatically shutting off.

Recently, iPhone customers in the country have been complaining about the problem to the China Consumers Association, the group said in a statement on Tuesday. The shutdowns occur when the phone’s battery charge drops to between 60 and 50 percent.

The problem will persist despite upgrading to the latest version of iOS. It will also occur in both cold environments and at room temperature. After the automatic shutdown, the phones will also fail to turn on without connecting to a power supply.

A “considerable number” of consumers have contacted the China Consumers Association, and many have the same problem, the group said. It made the statement as the local press in the country have written stories about the shutdowns.

So far, Apple hasn’t publicly commented on the matter.

Prior to Tuesday’s statement from the China Consumer Association, affected iPhone users in the country also took to local social media services to express their complaints.

“When the battery is at 60 percent it shuts down,” wrote one user on Sina Weibo. “On restart, the phone will display no battery. Then when I turn it on again, it will be normal, only to automatically shut down again.”

Local Chinese media have posted the letter the China Consumers Association sent to Apple. It asks that the company reply within 10 days.

The association is asking Apple what the exact problem is, whether the phone’s battery is responsible, and what steps the company will take to address the issue.