BTSC filed the lawsuit against the Bangkok Metropolitan Administration (BMA) at the Administrative Court.
The company is also in the process of collecting documents and other evidence to file a lawsuit claiming 20 billion baht from the BMA for its purchase of train operating systems for the extension.
The move comes after the BMA reportedly failed to meet a debt-repayment deadline in April.
Surapong said the overdue payment, totalling nearly 30 billion baht, had impacted business and forced BTS to borrow money. He added that the Green Line extension is still free to use in line with the BMA’s order, which had not changed.
“Whether they [BMA] decides to collect fares or not is not up to BTS. It is the BMA’s job to decide,” he added.