Foxconn, the world's biggest contract electronics maker, has admitted student interns worked shifts at a factory in China that were in violation of its company policies.
The firm, which makes products for some the world's biggest brands, has been under scrutiny for labour practices.
It had admitted to hiring underage interns at the same unit last year.
Foxconn said actions had been taken to bring the factory "into full compliance with our code and policies".
"There have been a few instances where our policies pertaining to overtime and night shift work were not enforced," the company said in a statement.
The manufacturing giant is owned by Taiwanese group Hon Hai Precision and employs about 800,000 workers around the globe.
Foxconn, while not a household name in itself for many consumers, is used by most of the big technology giants around the world, including Apple, Sony, Microsoft, HP, and Nokia.
It first came under scrutiny for its labour practices when 13 employees committed suicide at its Chinese plants in 2010.
The incidents raised concerns over working conditions at its units in China and drew attention to growing labour strikes.
For its part, Foxconn responded by raising wages, shortening working hours and employing counsellors on site.
It also installed suicide nets to factory living-quarters at its Shenzhen factory.
Also in 2010, Foxconn temporarily shut down a unit in India after 250 workers fell sick.
And in May 2011, two people were killed after an explosion at a company plant in Chengdu.