Apple Inc increased the number of audits into working conditions at major suppliers by more than 70% last year, according to its annual report, and conducted 393 audits of sites where over 1.5 million workers make its gadgets.
It found multiple cases of underage workers, discrimination and wage problems, and terminated its relationship with at least one supplier.
The company has been accused in recent years of building profits on the back of poorly treated and underpaid employees of Taiwan's Foxconn Technology Group.
Apple senior vice president of operations Jeff Williams said the company has increased efforts in two major problem areas: underage workers and limiting workers hours to 60 per week.
In one case the company terminated its relationship with a component maker after discovering 74 cases of underage workers. Williams said:
"We go deep in the supply chain to find it. And when we do find it, we ensure that the underage workers are taken care of, the suppliers are dealt with."