The Royal Forest Department on Thursday accused political activist Thanathorn Juangroongruangkit, his mother and his younger sister of illegally occupying more than 2,000 rai of forest reserve land in Ratchaburi province.
The complaint was filed on behalf of forests director-general Adisorn Nuchdamrong with the Natural Resources and Environmental Crime Suppression Division.
It accused Mr Thanathorn, founder of the Progressive Movement group, his mother Somporn and his younger sister Chanapan of illegally occupying connected blocks of land totalling 2,154 rai within a national forest reserve in tambons Rang Bua and Dan Thab Tako of Chom Bung district, Ratchaburi.
The department estimated the damage to the forest at 147 million baht, and planned to also file a civil lawsuit against the family.
Cheevaparp Cheevatham, director of the department's Forest Protection and Fire Control Office, said the three accused had 60 land right documents laying claim the forest land. He alleged that the documents were illegally issued.
Mrs Somporn had 53 title documents, Miss Chanapan five and Mr Thanathorn two, he said.
The forest reserve was declared in 1969, but the land right documents were issued from 1978 onwards, Mr Cheevaparp said. The land was developed as eucalyptus plantations.
Some land and administrative officials had been behind the issuance of the illegal documents, he alleged.
On Dec 30 last year, the Royal Forest Department accused Mrs Somporn of illegally occupying 440 rai of forestland, also in Ratchaburi.
The Royal Forest Department was checking title to hundreds of rai of more land that Mrs Somporn occupied in Ratchaburi, he said.
It is the latest in an on-going series of government attacks on Mr Thanathorn, who is seen as a political threat to the established elite.
The Constitutional Court disbanded Mr Thanathorn's Future Forward Party in February last year for accepting a 191-million-baht loan from him, considered an illegitimate source of funds. He and other party executives were banded from politics for 10 years.