Apple supplier Foxconn illegally hired students to work overtime to build the iPhone X, according to The Financial Times.

The factory reportedly hired 3,000 students from a local school in Zhengzhou, China as interns. They assembled the iPhone X in 11-hour work shifts; under Chinese law, students can only work eight hours a day. FT interviewed six of the 3,000 students, ages 17 to 19, who said the school forced them to work at Foxconn, even though iPhone assembly had nothing to do with their studies.

Apple and Foxconn did not immediately respond to PCMag's request for comment, but Apple told the FT it "confirmed the students worked voluntarily, were compensated and provided benefits, but they should not have been allowed to work overtime."

The report of the illegal overtime comes as Apple has been seeing high demand for the iPhone X. Pre-order sales for the device were "off the charts," according to Apple.

To build the iPhones, Apple supplier Foxconn hired hundreds of thousands of workers in China, but also brought in the student workers from local vocational schools as part of an "internship program," a practice which has drawn scrutiny from labor watchdogs like China Labor Watch, which investigates labor abuse claims at Apple supplier factories.

"When Apple's production demands it, Apple completely ignores the labor standards they have set," Li Qiang, executive director of China Labor Watch, wrote in an email.

The illegal overtime problems are also nothing new. Foxconn has been hiring student workers for years, but Apple still hasn't done enough to limit the work hours, according to Li. "Apple knew about the issue with student workers some time ago," he claimed. "The issue remains unresolved as the company has production targets to meet."