Cambodia, Laos and Vietnam have questioned Thailand's ability to host a regional summit next month because of the deepening political crisis in Bangkok.
The Foreign Ministry in Cambodia said on Wednesday that the prime ministers of the three countries, meeting in Vientiane, have formally asked the 10-member Association of South East Asian Nations whether the meeting should be postponed.
ASEAN is due to meet from 14-17 December to address regional measures to bolster the financial system and boost flagging economic growth.
The meeting was originally been scheduled to take place in Bangkok, but was switched to Chiang Mai because of trouble in the capital.
ASEAN members are: Brunei, Cambodia, Indonesia, Laos, Malaysia, Myanmar, Singapore, Thailand, Vietnam and the Philippines. The meeting includes the leaders of China, Japan, Australia, South Korea and India.