The kingdom's "royal insult" prisoners, locked up for breaking Thailand's most enduring taboo say that they face mistreatment from jail guards and are shunned even by common criminals.
They are viewed by their supporters as prisoners of conscience, and in most countries would never have been locked up.
But in Thailand they carry the stigma of flouting one of the nation's toughest and most controversial laws: defaming the monarchy.
"Some of the wardens took me to a different part of the jail and ordered other prisoners to beat me," said Thantawut Thaweewarodomkul, who is serving a 13-year term for posting online content deemed offensive to the royals.
The incident, which happened soon after he was incarcerated three years ago, left him with two black eyes, the 40-year-old told an AFP reporter who visited him in the high-security Bangkok Remand Prison.
The former administrator of the Nor Por Chor USA website, which has links to the "Red Shirt" protest movement loyal to ousted premier Thaksin Shinawatra, he was convicted under controversial lese majeste and computer crime laws.
He is one of nine lese majeste prisoners in the kingdom, according to the Office of the Human Rights Commission of Thailand, which says there were 241 cases under the law from 2007-2012, with an unknown proportion still under investigation.
Benjamin Zawacki, Southeast Asia researcher for Amnesty International, said lese majeste is seen as an "offence to society" and not just the four individuals it is designed to protect -- the Thai king, queen, heir or regent.
"Fellow prisoners, common criminals, look at them as somehow committing a crime that is different than what they have committed and somehow worse," he said. "It is not incredibly different than the way paedophiles are treated."
The authorities bear responsibility for the mistreatment of royal insult prisoners, many of whom are held without bail and are tried in secret on national security grounds, he said.
The royal family is an extremely sensitive subject in politically turbulent Thailand.
King Bhumibol Adulyadej, 84, is revered as a demi-god by many Thais, but he has been in hospital since September 2009.
Rights campaigners say the law has been politicised in recent years, with many of those charged linked to the Red Shirts, whose street protests in Bangkok in 2010 triggered the worst civil unrest in decades with about 90 dead.
Many Red Shirts seek the return of Thaksin, a former telecoms tycoon who was toppled by royalist generals in a coup in 2006 and lives overseas to avoid a prison sentence for corruption, which he contends is politically motivated.
Thaksin's sister Yingluck Shinawatra leads a government elected last year, but lese majeste cases have continued under her and she has dismayed activists since becoming premier by ignoring calls for reform of the law.
Prisoners say, however, that their conditions have improved under the current administration.
Daranee Charnchoengsilapakul, a hardcore Red Shirt serving a 15-year term for defaming the royals during political speeches, no longer has to guess who her visitors are in order to see them, according to one of her friends.
But "not long ago she told me that she was still being beaten by some wardens", her brother Kittichai Charnchoengsilapakul told AFP. "They want to bully her."
In May Ah Kong, a 62-year-old grandfather, died in custody while serving a 20-year sentence for allegedly sending text messages to an aide of former Prime Minister Abhisit Vejjajiva that were deemed insulting to the royal family.
An autopsy showed the inmate -- known in Thailand as "Uncle SMS" -- had been suffering from liver cancer.
But the death of one of the country's best known lese majeste prisoners generated a rare outcry among ordinary Thais.
His wife Rosmalin Tangnoppakun said prison was "hard" on her husband, but neither the authorities nor his family knew he was suffering from the disease, and Ah Kong did not talk about conditions inside the jail.
"He did not really tell me because he was afraid that I would be worried about him," she said.
Sorasit Chongjaroen, the superintendent of the Bangkok Remand Prison, denied there was mistreatment of inmates.
"There is no such thing -- no beatings here," he told AFP.
As for medical care at the prison, "it cannot be compared with hospitals outside anyway," Sorasit added.
Amnesty views people incarcerated solely under the lese majeste law -- which carries a maximum penalty of 15 years in jail on each count -- as prisoners of conscience.
"If that is the only law under which they have been in prison they should be released. Treatment in prison, that's a conversation we shouldn't even be having," said Zawacki.
Sukanya Pruksakasemsuk, whose husband Somyot is facing charges over two articles published in his now-defunct Red Shirt magazines, said the law itself was futile.
"You can physically put them in prison, but you cannot jail their thoughts," she told a press conference last month.