The latest report into Foxconn, first detailed in the Guardian, alleges hundreds of school students have been drafted in from local vocational schools to help fulfil orders.
The report alleges the so-called interns are paid as little as $1.42 (£1.18) an hour, or about $248 (£205) a month, for their time. The teenagers were reportedly expected to work 10 hour shifts, including two hours overtime, six times a week.
China Labor Watch say many students sleep in shared dormitories and face pressure from teachers, who are also recruited, to work hours that violate labour regulation.
"If interns were unwilling to work overtime or night shifts, the factory would arrange for teachers to pressure workers," the report says. "For interns who refuse to work overtime and night shifts, the factory requests teachers from their schools to fire them."
Activists also make allegations of physical and verbal abuse by teachers at the site. The intern's schools are compensated financially for their time, the report adds.
One student, a 17-year-old named as Xiao Fang, was quoted by China Labor Watch describing her role putting protective film over about 3,000 Echo Dot devices a day.
The report says she found working in the "very bright" and "hot" factory very tiring and she did not want to work overtime.
"The teacher went to speak to Xiao Fang and said that if she doesn't work overtime, she can't intern at Foxconn and this will affect her graduation and scholarship applications at the school etc," the report says.
"With no choice, Xiao Fang could only endure this."
Amazon, owned by the world's richest man Jeff Bezos, said in a statement to the BBC it does not tolerate violations to its supplier code of conduct.
"We are urgently investigating these allegations and addressing this with Foxconn at the most senior level," the statement said. "Additional teams of specialists arrived on-site this wee k to investigate, and we've initiated weekly audits of this issue."
"There have been instances in the past where lax oversight on the part of the local management team has allowed this to happen and, while the impacted interns were paid the additional wages associated with these shifts, this is not acceptable and we have taken immediate steps to ensure it will not be repeated," they said.
Foxconn also reportedly pledged to review salaries and increase regular worker levels.