Striking Thai train drivers went back to work Thursday after a one-day walkout that left thousands of people stranded, a railway official said.

The drivers returned following assurances from management at the State Railway of Thailand (SRT) that a free trade pact with Japan, allowing private companies to operate on railways here, would not threaten their jobs.

The trade agreement, which tears down most tariffs between the two countries, went into effect Thursday.

The SRT also promised not to punish any of the striking drivers.

The management "agreed not to press either civil or criminal charges against striking workers," said SRT spokesman Pairat Rojcharoenngam.

Thousands of passengers were affected Wednesday when drivers refused to work on express trains in the south of Thailand and in the northern city of Chiang Mai.

International services connecting Thailand with Butterworth in northern Malaysia were also hit by the rare wildcat strike.

Union officials on Wednesday said the strike was prompted by mismanagement of the railways.

The State Railway Workers Union of Thailand issued a statement saying the strike was to protest incompetence by SRT executives and the board, resulting in losses of 23 billion baht (725 million dollars).

Pairat said the state railway operator has incurred losses worth 40 billion baht.