There were 69 Bolivians on the Armonía ship, operated by MSC Cruises, whose Schengen visas had been falsified, the company said, confirming reports in Spanish media.
The group of Bolivians, which included families with children, had embarked in Brazil for the journey to Barcelona, where their voyage was to end. But, following visa checks, they were not allowed to leave the ship to go ashore like the other passengers.
Schengen visas allow their holders to travel among nearly 30 European countries.
Meanwhile, the Armonía had planned to continue its journey on Tuesday through the Mediterranean for other passengers, but the vessel has instead been held up in Barcelona pending the investigation.
Some relatives of the Bolivians on board who live in Spain told Spanish media that the people had been victims of a scam.
They said an agency in South America had offered the passage and visas online and charged up to $10,000 per person. This agency also cancelled return flight tickets that had been promised after the cruise ship left Brazil for Europe, La Vanguardia newspaper quoted relatives as saying.
However, the police have not ruled out the possibility that the Bolivians actually wanted to enter Spain illegally using knowingly forged documents.
It was unclear when the ship would be able to continue its journey and what would happen to the Bolivian passengers.
