A court in Thailand sentenced a woman to 43 years and six months imprisonment for violating the nation's strict law on defaming or insulting the monarchy, Insider reported on Wednesday, citing legal counsels in what could be the harshest sentence ever passed under the country's lese-majesty law.

A former civil servant, Anchan Preelert, who is in her mid-60s, was accused of posting audio clips to YouTube and Facebook with comments authorities considered critical of the royal family, the Thai Lawyers for Human Rights said.

Preelert was first arrested in 2015 after her involvement with the underground podcast host known as "DJ Banpodj", a vocal critic of the royal family.

Under Thailand's lese-majesty law, anyone who "insults, defames or threatens the king, queen, heir apparent or regent" can face between three to 15 years in prison on each charge. Preelert was found guilty on 29 counts of violating the law.

The Thai court initially announced she would be serving 87 years in prison, but reduced it by half because Preelert pleaded guilty to the charges, TLHR said.

Human rights organizations denounced the case, which follows months of demonstrations that have seen unprecedented public anger of the royal family and demands an end to the ruthless law, also known as Article 112 of the Penal Code.

Preelert thought what she had done "was nothing" as there were so many people "who shared this content and listened to it. The guy (who made the content) had done it for so many years," she said before her sentencing, the Associated Press reported.

The court ruling comes at a time when authorities try to clamp down on an unprecedented pro-democracy movement whose demands include reforms to the government and the powerful monarchy.

Protesters, who massed up in the tens of thousands last year, have condemned King Maha Vajiralongkorn and questioned the monarchy's vast wealth and influence.

Titipol Phakdeewanich, a Ubon Ratchathani University political analyst, said Preelert's sentencing could be "politically motivated" to intimidate activists.

"Today's court decision is shocking and sends a spine-chilling signal that not only criticisms of the monarchy will not be tolerated, but they'll also be severely punished," Sunai Phasuk of Human Rights Watch said in remarks quoted by The Telegraph.