In 2006, Thaksin sold shares Shin Corp, a telecommunications firm he founded, to Singapore's Temasek, raising concerns about a conflict of interest as well as allegations of tax evasion.

At the time, the former premier said the transaction was compliant with rules, but the sale ignited protests in Bangkok that eventually led to the army deposing him and seizing power later that year. 

"This matter must proceed based on the judgement," Finance Minister Ekniti Nitithanprapas said on Tuesday.

"The Revenue Department are examining the details," he told reporters when asked when the taxes would be collected.

The ruling is the latest blow against the polarising billionaire, who is currently serving a one-year prison term for a separate matter. 

Thaksin's representatives declined to comment when contacted by Reuters. 

In August, Paetongtarn Shinawatra, his daughter, was dismissed by court order over an ethics violation that stemmed from a leaked phone call between her and Cambodia's former leader Hun Sen. 

In May, his sister, former Prime Minister Yingluck Shinawatra, was also ordered to pay $305 million in damages over a botched rice scheme. 

She was sentenced to five years to prison in absentia for the case in 2017 and has been living overseas to avoid prison. 

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