The organisers of the Miss Universe contest are trying to limit the damage after photos of bikini-clad contestants were taken near a Thai Buddhist temple.
Other parts of the pageant have proved less controversial
The offending images show contestants in a boat on a Bangkok river, with the famous Wat Arun in the background.
Pageant organisers have apologised for the incident, which has offended Thai Buddhist leaders.
But Thai Prime Minister Thaksin Shinawatra urged people not to over-react.
"I think the contestants did not intend to insult Thai culture. They just wanted to shoot pictures of beautiful places, but did not realise that the temple is sacred for Thais," he said.
The 81 contestants, all winners in their own countries, are vying to win the Miss Universe title.
The photographs were part of a three-week prelude to the main competition on 31 May.
Thailand hopes the pageant will boost its tourism sector, which was badly hit by last December's tsunami.
'Mark the country with sin'
The president of the pageant, Paula Shugart, said the incident at Wat Arun was unfortunate and would not happen again.
"We knew that if we had any visits to the temple, we knew how the women had to dress. This happened to be out on the river and unfortunately it appeared in the background," she told Reuters.
"We would never, ever do anything to intentionally offend anyone here."
But Preecha Kanthiya, director-general of the Culture Ministry's religious affairs department, said pageant organisers should be more aware of Thai sensitivities.
He added that if the organisers wanted to promote Thailand, "they should ask the contestants to wear Thai traditional costumes".
"This is the time of Visakha Bucha, when we are reminded of Lord Buddha's teachings," added Phra Thep Dilok, the head of the National Center for Buddhism Promotion.
"We have allowed this thing which will mark the country with sin for a long time," he told Reuters.