Human rights groups and labor organizations are urging Thailand's military government to cancel a state-sanctioned project to put prisoners to work on Thai fishing boats to fill a labor shortage.

In a letter addressed to coup leader-turned-Prime Minister Prayuth Chan-ocha, some 45 organizations say the pilot project poses "a serious threat" to the human rights of prisoners.

Thailand's fishing industry has been criticized for years because boat crews are often migrants from neighboring countries forced into virtual slavery on vessels at sea.

Last year, the United States demoted Thailand to the lowest level in its annual rankings of governments' anti-human trafficking efforts, principally over its failures to do enough to stop abusive practices in the Thai seafood industry.