Japan's labor ministry says about 70 percent of the companies that accept foreign technical trainees were found to have committed legal violations last year.
Japan has a system designed to enable trainees from developing countries to learn skills, technologies, and expertise while working in the country.
The Immigration Services Agency says that as of last December, Japan had more than 370,000 such trainees.
In response to reports and consultation requests from trainees, the labor ministry conducted on-the-spot investigations into 8,124 firms nationwide last year by sending labor standards inspectors.
The inspections found that 5,752 business operators, or 70.8 percent of those inspected, violated the Labor Standards Law.
24.3 percent made violations related to safety management at workplaces.
15.7 percent illegally forced interns to put in time longer than the cap agreed between workers and management.
15.5 percent failed to pay interns for overtime work.
Last year, the Labor Standards Inspection Offices received 192 petitions from trainees, calling for rectifying unpaid overtime allowances and other irregularities -- an increase of 85 from the figure in 2019.
The ministry says a recent business slump due to the coronavirus pandemic may be a factor behind the increase in the number of failures to pay for overtime.
It plans to carry out more such inspections and issue orders if need be.