A Japanese doctor is warning Vietnamese considering traveling to Japan to work as vocational trainees to think twice, saying the system amounts to “slavery” and uses the country’s positive image to take advantage of those who enroll.

Junpei Yamamura, a doctor at Minatomachi Medical Center in Yokohama, produced a 13-minute video in Vietnamese after visiting the Southeast Asian country between May and June to interview four people who returned from Japan after having bad experiences with the vocational trainee system.

The interviewees, including a 24-year-old man who lost sight in his left eye after an accident while working at a construction site in Japan, speak of the hardships experienced while working as trainees.

The man said that after the accident he was forced to leave Japan by the institution which was overseeing him and other Vietnamese trainees. He said there were inadequate procedures to allow him to make an insurance claim for his injury and he had to file for compensation again upon returning to Vietnam.

Other episodes unveiled in the video include alleged cases of physical violence and unpaid overwork.

The video was uploaded on YouTubeby the Lawyers Network For Foreign Workers, a group that has been working in collaboration with Yamamura in helping foreign residents of Japan.

According to the Health, Labor and Welfare Ministry, there were about 229,000 foreign vocational trainees in Japan as of the end of 2016. Vietnamese accounted for the largest single group, at 88,000, followed by Chinese at 81,000, Filipinos at 23,000 and Indonesians at 19,000.

While the system for inviting foreign people to work at Japanese companies as trainees was established with the aim of helping them acquire skills that can be used to develop their own countries upon returning home, there have been cases of Japanese companies abusing the system as a source of cheap labor.

According to labor ministry data released in August, a record 4,004 employers who accepted trainees from abroad under the Technical Intern Training Program violated labor laws in 2016 — the most since 2003.

The cases marked an increase of 309 from the previous year, reflecting a rise in number of trainees. Violations related to illegally long working hours accounted for 24 percent of the total, while failure to take necessary safety measures came next at 19 percent, followed by cases of unpaid overtime at 14 percent.

The program is to be drastically reformed next month. The training period is to be extended from three years to five, and a watchdog will be established to check whether companies are in compliance with appropriate pay offers.

Foreign trainees work in various sectors.

In the manufacturing field, participating companies include machinery makers, construction firms and food processors, said an official with the Japan International Training Cooperation Organization, which connects foreign trainees with Japanese companies.

Yamamura said Japan should “accept foreigners as workers, not as vocational trainees.”