A group of elderly bridge players in the Thai resort town of Pattaya were surprised by a visit from the police on Wednesday.
Thirty-two foreigners, including British, Swedish, Norwegian and Australian citizens, were arrested during the anti-gambling raid.
They said they were not playing for money, but were held for possessing too many unregistered playing cards.
Thailand's military rulers have vowed to crack down on corruption and crime.
The players were released on bail on Thursday, after 12 hours in custody.
In addition to 12 Britons, those arrested included three Norwegians, three Swedes, two Australians, a German, a Dane, a Canadian and a New Zealander, AFP news agency reported.
An 84-year-old Dutch woman was also among those held, local paper Pattaya One reported.
Police said they raided the bridge club after its anti-corruption centre received a tip-off.
The members had broken a 1935 law, the Playing Cards Act, which prohibits individuals from possessing more than 120 playing cards, Pattaya One said.
The president of Thailand's bridge league has travelled to Pattaya to explain to police how bridge is played, the paper added.
Thailand has strict anti-gambling laws, with nearly all forms of gambling prohibited.