Authorities in the south central province of Binh Thuan on Monday said four boats with 33 fishermen had been arrested by Indonesian officials early this month.
The boat owners have been identified as Phan Hanh, Nguyen Phi Yen, Le Hung and Phan Thi Son.
They were arrested while fishing on the water border between Vietnam and Indonesia.
Only 16 of the fishermen have been identified as 17 others were working without a labor contract.
Binh Thuan officials said they have not contacted with Indonesia officials but only been informed by the sailors via their walkie-talkie.