The Toyota Avensis with Latvian license plates was stopped in the district of Lazdijai, which borders Poland, on Thursday.
The 26-year-old Latvian driver had four passengers in wet clothes in his car.
Three of them, including two men aged 18 and 38 years and a women aged 19 years, had Vietnamese passports. The fourth passenger had no documents, but said he was a 21-year-old Vietnamese national.
There were no Schengen visas in the Vietnamese passports.
A pre-trial investigation has been launched into unlawful transportation of persons across the state border, an offense that is punishable by up to six years in prison.