Thai share prices closed 0.73 percent lower on Tuesday after authorities ordered that shares in Thai Petrochemical Industry could only be acquired with cash, dealers said.
They said the new rule, ordered by the Thailand Securities Finance Corp, led to a sell down in energy stocks, resulting in the benchmark closing lower.
Prior to the rule change investors in Thai Petrochemical, the kingdom's biggest corporate defaulter, could acquire the company's shares through a combination of cash and loans.
The Stock Exchange of Thailand (SET) composite index shed 5.15 points to 695.60 and the blue chip SET 50 index fell 4.18 points to 487.75.
Turnover stood at 2.0 billion shares worth 11.4 billion baht (284 million dollars) traded. Losers outnumbered gainers 215 to 90, with 105 stocks unchanged.
"The change prompted investors to sell shares in Thai Petrochemical and it spread to selling of other energy shares," said Kanang Duangmanee, a researcher at Kasikorn Research Center.
Thai Petrochemical is undergoing a major restructuring after collapsing during the 1997 Asian financial crisis with debt mounting to 2.7 billion dollars, becoming Thailand's biggest corporate defaulter.
The finance minister said last week the company would likely complete its restructuring by early next year.
Among major shares, PTT fell 4.00 baht to 224.00 while its subsidiary PTT Exploration and Production dropped 8.00 to 432.00.
Shares in Thai Petrochemical fell 0.40 to 14.60 and Thai Oil declined 1.50 to 69.50 with National Petrochemical falling 2.00 to 128.00.
Thai Airways International rose 0.25 to 39.75.
The Thai baht closed on Tuesday at 41.20-22 to one dollar, against Monday's close of 40.98-41.07. Against the euro, the Thai unit closed at 48.30-35, compared with Monday's 48.31-67.