Seven years ago, Apple made a staggering discovery: Among the employees at a factory in China that made most of the computer ports used in its MacBooks were two 15-year-olds. Apple told the manufacturer, Suyin Electronics, that it wouldn’t get any new business until it improved employee screening to ensure no more people under 16 years of age got hired.

Suyin pledged to do so, but an audit by Apple three months later found three more underage workers, including a 14-year-old. Apple, which has promised to ban suppliers that repeatedly use underage workers, stopped giving Suyin new business because of the violations. But it took Apple more than three years to fully cut its ties with Suyin, which continued to make HDMI, USB and other ports for older MacBooks under previous contracts. A person close to Suyin, which is headquartered in Taiwan, said that the company hadn’t intentionally hired underage workers and that it had passed Apple’s audits in later years.