Manop Saejie, president of a tour guide association in Chiang Mai said he and his friends are licensed tour guides.
However, in recent weeks groups of Chinese staying in Thailand and Chinese students were illegally working as guides in the province, he said.
The Chinese had stolen their customers, Manop said, adding that foreigners are prohibited from working as tour guides. Training is also required to get a license.
He said that illegal tour guides also give inaccurate information about Thai culture. Tourists are charged high prices, and this would earn Thai tourism a bad reputation.