Apple said it found more than a dozen serious violations of labour laws or Apple's own rules at its suppliers that needed immediate correction.
The findings were outlined in a company report on audits of 102 supplier facilities conducted in 2009. That was a year in which questions about the practices of one of Apple's suppliers came into focus after the suicide of a Chinese worker who held a sensitive job handling iPhones.
Along with many other technology companies, Apple, based in Cupertino, California, relies heavily on foreign contractors to build its products. Monitoring their labor practices be difficult, and Apple has caught heat in the past on this issue.
The company said in its latest report that "by making social responsibility a fundamental part of the way we do business, we insist that our suppliers take Apple's code as seriously as we do."
Apple said it found 17 "core" violations, the most serious type.
Those included three cases of underage workers being hired; eight instances of workers paying "recruitment" fees that were above the legal limits in those countries; three cases in which suppliers used non-certified vendors to dispose of hazardous waste; and three others in which the companies gave false records during the audits.
In the cases involving underage workers, Apple said three facilities had hired a total of 11 workers who were 15 years old in countries where the minimum employment age is 16. Apple noted that the workers were no longer underage or weren't working for the facilities anymore when the audits were undertaken.
Apple has been pressured before to answer questions about its suppliers' practices.
Last July, a 25-year-old Chinese worker whose job involved shipping iPhone prototypes to Apple killed himself by jumping from the 12th floor of his apartment building amid an investigation into a missing iPhone. The worker, Sun Danyong, worked for the Foxconn Technology Group, a Taiwanese manufacturer that has long been one of Apple's key suppliers.
The suicide, and allegations that Foxconn security guards roughed up the worker before his death, prompted a reply from Apple that all of its contractors "must treat workers with respect and dignity."
In 2006, Apple found that workers in a Chinese iPod factory were in many cases exceeding the company's limits for overtime. Apple ordered the factory to comply with its limits. Apple was responding to news reports at the time that workers at the factory were paid as little as $50 a month and were forced to work 15-hour shifts.