DOL investigators discovered that the firm had employed 1,482 teenagers, “primarily as interviewers” at 11 call centres, breaking time and hours standards in the process. Violations included children working for more than three hours on a school day and more than eight hours at weekends.

Three of the workers were 13 years old, which is a violation of US labour laws stating that children of that age can only work on farms. The rest were aged between 14 and 15, and their employment was subject to hour and time standards.

Officials said that the $552,750 fine was “among the highest ever assessed by the department”, and that violations occurred across six states.

Western Wats has disputed the DOL’s findings and already launched an appeal.

The firm’s attorney Stacy Jenkins said in a prepared statement: “Western Wats vehemently denies the extent and severity of the claimed violations. In all cases, the work was performed in a safe environment and provided an excellent employment experience. While it is possible that technical violations did occur, it is appropriate to withhold judgement until the appeal process is complete.”

In a statement, Secretary of Labor Hilda Solis said: “This investigation reflects the Department of Labor’s ongoing effort to strengthen workplace protections that promote the safety and well-being of young workers.”

Western Wats had not returned calls seeking comment at the time of going to press.