The Justice Ministry revealed Friday that at least four construction companies have used foreign trainees in radioactive cleanup work related to the triple meltdown at the Fukushima No. 1 nuclear power plant, which occurred in 2011.

The interim report of the ministry’s probe, covering 182 companies with foreign trainee programs as of June 29, said one of the four companies, based in Iwate Prefecture, has been banned from accepting foreign trainees for five years.

The other three firms — two in Fukushima Prefecture and one in Chiba Prefecture — are still under investigation. The names of the companies were not revealed.

The ministry plans to compile a full report covering 1,002 companies in eight prefectures, including Miyagi, Ibaraki, Tochigi, Gunma and Saitama, this fall.

The research started in the wake of a government announcement in March banning the use of foreign trainees in work to remove radioactive contamination. The government says such work is not consistent with the true purpose of the foreign trainee program.

The Technical Intern Training Program was introduced in 1993 with the aim of transferring skills to developing countries. But the scheme has drawn criticism both at home and abroad as a cover for importing cheap labor for the manufacturing, construction and other industrial sectors, where blue-collar workers are in short supply.

The issue came to light in March, when a Vietnamese trainee at an Iwate-based construction firm revealed he had been assigned to take part in radioactive decontamination work without being given adequate explanation.

According to the Tokyo-based Zentoitsu Workers Union, which represents the man, he was supposed to conduct decommissioning and public engineering work but was instead assigned to clean up contaminated areas in Fukushima, exposing him to radiation.

Companies accepting foreign workers under the trainee system are required to submit a detailed plan regarding their training programs to a Justice Ministry body tasked with overseeing them.

But in reality, some companies assign foreign trainees to duties that were not written in the document, said Ippei Torii, chairman of the board of Solidarity Network with Migrants Japan, a support group for foreign workers. He added that similar cases of abuse took place in many parts of the country before the ministry began its investigation.

But “if you look at actual construction sites, no workers are assigned to work only on one task (regardless of whether they are Japanese or non-Japanese). They are all asked to do multiple different tasks at first so as to find their strong areas and to gain skills in those fields,” Torii said.

“The biggest problem is that the system itself does not reflect reality,” he said. “In that sense, I think companies are also victims of this program” as some of them hire foreign trainees who are introduced by malevolent brokers, without being informed about detailed rules of the program, he added.

In May, six people under a foreign trainee program were found to have participated in construction work at the Fukushima No. 1 plant despite a ban on trainees working at the crippled facility. Tokyo Electric Power Company Holdings Inc., the operator of the Fukushima plant, said they were hired by one of its subcontractors and sent to take part in groundwork without receiving any training on how to protect themselves from radiation.