Apple has published a list of its suppliers for the first time as it looks to head off criticism over how workers are treated.
The company also said it has increased its inspection of factories in a bid to ensure proper working conditions for suppliers' employees.
Apple came under fire last year after workers committed suicide at factories owned by its supplier Foxconn.
The tech giant had so far kept details of its supply chain secret.
"Apple is committed to driving the highest standards for social responsibility throughout our supply base," the company said in its supplier responsibility report.
"We require that our suppliers provide safe working conditions, treat workers with dignity and respect, and use environmentally responsible manufacturing processes wherever Apple products are made."
Apple said it conducted 229 audits at different factories over the past year, during which it uncovered various cases of non-compliance of labour rights.
It said that it found that employees at 93 factories had exceeded their "weekly working hour limits", while there had been payment violations at 108 facilities.
The company said it also found that five factories had employed underage workers, though that was due to "insufficient controls to verify age or detect false documentation".
Apple said that it was working closely with its suppliers to ensure that these issues were sorted out.
"I would like to make a significant improvement in the overtime area," said Tim Cook, chief executive of Apple.
"I would like to totally eliminate every case of underage employment," he added. "This is something we feel very strongly about and we want to eliminate totally."
Apple said it was also educating the suppliers' employees about their rights.
"Apple-designed training programs educate workers about local laws, their fundamental rights as workers, occupational health and safety, and Apple's Supplier Code of Conduct."