Foxconn, the Taiwanese electronics maker that supplies companies such as Apple and Sony, has admitted that student interns at one of its factories in China have worked shift patterns that are in violation of company policies.

Local media alleged the company, listed as Hon Hai Precision Industries on the Taipei stock exchange, had forced thousands of students from the Xi'an Institute of Technology to work at the plant assembling parts of Sony's PlayStation 4 games console. Foxconn responded with a statement Thursday evening that it had conducted an internal investigation at its Yantai campus, which is located around 600 kilometers from Beijing.