Thailand is a major manufacturing hub in the competitive Southeast Asian auto market.

Boonyeun Sookmai, coordinator for Labor Relations Group for Eastern Thailand, told Reuters more than 350 employees and contractors at General Motors (Thailand) were affected by the cuts, which employees and contractors were told about this week.

GM did not confirm the number of layoffs but said in a statement it was "necessary to right-size" its operations.

"We are taking every measure to support employees whose roles are impacted," the statement said.

It added: "There is no change to our ongoing business in Thailand - we continue to build and sell world-class trucks, SUVs and engines for Thailand and the world."

The company has about 1,900 employees in Thailand, according to the Bangkok Post, in operations that include a vehicle assembly plant that produces 180,000 units per year.

Thailand is a regional vehicle production and export base for the world's top vehicle manufacturers, including Toyota, Honda and Harley-Davidson.

The auto industry accounts for about 10% of the Thai economy and has been one of a few growth drivers at a time of falling exports.

Previously booming domestic auto sales have cooled in Thailand with finance firms using stricter lending criteria.

Thai domestic car sales contracted in July for a second straight month, down 1.1% from a year earlier.

GM has two plants in Rayong, a province on Thailand's eastern seaboard, for vehicle assembly and another for powertrain and engines. Its vehicle assembly plant began operations in 2000 and the latter in 2011.

The plants in Thailand produces vehicles for the domestic market and export under the Chevrolet and Holden nameplates.