Police are considering a complaint of mistreatment to three foreign exchange teachers arrested and held for eight hours before release without charge.
The three men from Zanzibar, in Tanzania, were arrested while shopping for presents in Cardiff.
Habib Seif Ali, Seif Haji Jaha and Haji Hassan Chum said they were handcuffed and strip-searched by police.
South Wales Police said they could not comment, but they had been arrested on suspicion of fraud before being freed.
The three men were in Wales for a teacher exchange project between schools in south Wales and Zanzibar.
The project, which has been running for 10 years, is overseen by the Pembroke-based Sazani Associates, and funded by the UK Department for International Development through the British Council.
Cathryn Al Kanaan, who runs the project, said: "The three men said they felt they had been treated like slaves, just handcuffed and shoved into the back of a police vehicle.
"They feel totally embarrassed and ashamed about the incident."
She has made the complaint to police on behalf of the three men, who have now returned home. She said the Zanzibar Ministry of Education was putting together a complaint to send to the UK Government.
In the early afternoon on 18 September, the three men were in Cardiff city centre, shopping for mobile phones and cameras to take home as presents to family.
In recorded statements given to a staff member of Sazani Associates back in Zanzibar, the three men said the experience had been "shameful" for them.
Haji Hassan Chum said: "We decided to ask a policeman to help us, because we needed a phone to be unlocked and wanted directions.
He said they were handcuffed and were told they were "thieves".
The men, who teach maths, geography and history, said they were all fingerprinted, while Mr Jaha said he also had a DNA saliva swab taken without explanation. He said he was also denied food, water and blankets, which the other two men received.
While they were held separately in cells, police officers searched the men's Cardiff hostel and took Mr Ali's passport, said Ms Al Kanaan.
She added: "In Zanzibar Britain is held up as country where things are done properly and where people are treated with respect.
"Those illusions have been shattered."
The three men said they explained to police they were in Wales as part of a teacher exchange programme. At about 0200BST on the Sunday they were released without charge, but the men said they were offered no assistance to find their way back to their hostel and had to walk through the city for an hour to find it.
Their group was scheduled to leave Cardiff to fly back to Zanzibar that day and it was while packing that Mr Ali said he realised his passport was missing.
Ms Al Kanaan said the teacher was accompanied to the police station by David Edwards, a former police officer and now a teacher who had been working with the men.
"He managed through knowing police procedure to get the passport found," she said.
But she said Mr Ali was kept waiting three hours for the document.
Ms Al Kanaan added: "I feel ashamed to be Welsh. These men did nothing wrong.
"I really hope teachers in Zanzibar aren't now discouraged about coming to Wales."
A spokesman for South Wales Police said it was inappropriate to comment as an investigation was ongoing.
The spokesman said: "At around 5pm on Saturday, 18 September South Wales Police received a report of a skimming machine at an ATM in Working Street, Cardiff.
"A mobile phone had been attached to the cash machine filming users entering their personal identification number (PIN) as well as a device at the card entry point.
"Officers attended and at around 5.30pm three men aged 51, 28 and 20 were arrested on suspicion of fraud.
"They were taken into custody but following further inquiries were released without charge in the early hours of Sunday, 19 September."