Thai tax authorities have sent ousted former prime minister Thaksin Shinawatra a whopping 17 billion baht ($494 million) tax bill over the sale of shares in a telecoms company more than a decade ago, his lawyer said on Tuesday.

The claim is over the sale of shares in Shin Corp. to Singapore's Temasek Holdings [TEM.UL].

Thaksin's legal team would appeal to the revenue department within 30 days, his lawyer, Noppadon Pattama, told reporters.

"We need to exercise our right to appeal to show that no legal miracle can happen to collect tax from Dr Thaksin," he said.

Allies of Thaksin say the new tax claim is politically motivated. He has lived in exile since being overthrown in 2006 to avoid corruption charges, but his populist movement remains at the heart of political division in Thailand.

Defence Minister Prawit Wongsuwan told reporters the tax claim was not aimed at bullying the Shinawatras.

A court ruled against an attempt by tax authorities to claim 12 billion baht ($350 million) from the share sale from Thaksin's children in 2010, Noppadon said. The court said they could not be taxed because the shares were owned by Thaksin and his wife, he said.

Noppadon said that the sale of the shares was tax exempt because it was done through the stock exchange.

The army overthrew the government led by Thaksin's sister, Yingluck Shinawatra, in 2014 in the name of ending political turmoil.

Last month, the junta started reconciliation hearings with political parties ahead of elections that could happen as early as next year, but those talks do not touch on Thaksin's fate.