The Apple supplier Foxconn has admitted to using illegal intern labour to assemble the iPhone X.

Students said they worked 11-hour days, which is a breach of Chinese labour law.

The scandal comes after Apple reportedly faced delays in getting the iPhone X to customers.

The Apple supplier Foxconn has said it will stop using illegal intern labour in its factories that are used to assemble technology products for some of the world’s biggest companies, according to a report by BBC News.

Foxconn’s use of interns on its production lines was first reported by the Financial Times. Six students told the newspaper that they regularly worked 11-hour shifts assembling Apple’s new iPhone X, which is a breach of Chinese labour law. The Financial Times said a group of 3,000 interns worked in Foxconn’s factories.

The students, who were reportedly ages 17 to 19, told the Financial Times that their work at Foxconn was work experience that they had to do to complete their education.

Now, Foxconn has told BBC News it has ended its practice of letting interns work overtime. The company reportedly said it took “immediate action to ensure that no interns are carrying out any overtime work,” and it said interns represented “a very small percentage” of its overall workforce.

Apple told BBC News it was “dedicated to ensuring everyone in our supply chain is treated with the dignity and respect they deserve.” It continued: “We know our work is never done and we’ll continue to do all we can to make a positive impact and protect workers in our supply chain.”

It’s an embarrassing story for Apple, which has regularly faced criticism over the supply chain of its products. Apple had to ask the Chinese mining company Huayou to stop using child labour after Sky News found it was using children as young as 4 to mine for the material.

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Foxconn has faced its own issues in the past: In 2010 a series of employees died in suicides after working long hours in the factory, which eventually led the company to erect suicide nets on its buildings designed to prevent future deaths.

The iPhone X faced production problems

The KGI Securities analyst Ming-Chi Kuo covers Apple’s supply chain in Asia and regularly covered delays with the iPhone X. He said Apple faced shortages on key components of the device, which meant it struggled to get the phones it needed ready for when it went on sale.

Apple CEO Tim Cook was asked about the potential of delays to the iPhone X in an interview with BuzzFeed. The executive gave a rather diplomatic answer: “We’ll see what happens, but we’ll be working as hard as possible to make as many as possible.”