Australia will question Thailand about its royal defamation laws at a United Nations human rights review this week, after an activist's mother was charged for receiving Facebook messages.

Key points: Woman faces three to 15 years jail

Woman faces three to 15 years jail Woman's son is a political activist

Woman's son is a political activist 70 lese majeste cases recorded in Thailand since 2014 coup

Thailand's military government claims Patnaree Chankij's failure to reprimand the person who sent her the messages amounts to royal defamation, a crime punishable by 15 years in jail.

Human Rights Watch said it marked a "new low" in the misuse of Thailand's strict lese majeste law, while others say it is a form of harassment.

"I think this arrest is political, the target is actually [Ms Patnaree's son] Ja New because he agitates against the coup," said Anon Nampha, from Thai Lawyers for Human Rights.

The United Nations also said it was "deeply concerned" about the case.

"We have concerns that the law is being interpreted this way and are worried that this could open the door to even more prosecutions," Jeremy Laurence, spokesman for the UN Office of the High Commissioner for Human Rights, in Asia, said.

"Since the military coup in 2014, we've documented 70 cases involving this [lese majeste] law," Mr Laurence said.

"In most instances it's been the military pressing the charges, and prosecuting and then dishing out the punishment in a military court."

Thailand faces human rights grilling in Geneva

A deep reverence for King Bhumibol Adulyadej is almost universal in Thailand, where the ailing monarch will soon mark 70 years on the throne.

The King has never personally filed a lese majeste case and has even encouraged criticism, but he is now seriously ill and has not spoken publically for many months.

Some rights groups argue cases filed on behalf of the palace have been used to attack opponents and silence critics.

Australia will press Thai officials about the use of the laws during a United Nations periodic review of human rights in Geneva review tomorrow.

According to advance questions posted on a UN website, Australia will ask two questions:

What current screening mechanisms exist to ensure that the prosecution of cases under Article 112 of the Criminal Code (the lese-majeste law) is consistent with Thailand's international human rights commitments?; and

What current screening mechanisms exist to ensure that the prosecution of cases under Article 112 of the Criminal Code (the lese-majeste law) is consistent with Thailand's international human rights commitments?; and Has consideration been given to establishing or strengthening inter-agency screening processes for cases brought under Article 112 of the Criminal Code to ensure that the fundamental right to freedom of expression and opinion is upheld?

'The evidence against her is weak'

Patnaree Chankij hugs her son, Ja New. ( ABC News: Liam Cochrane )

Patnaree Chankij's son is Sirawith Seritiwat, better known as Ja New.

The 22-year political science student is a leader with activist groups Resistant Citizen and New Democracy Movement, and has become one of the most-recognisable faces of dissent against Thailand's military junta.

A graphic revealed by Thai soldiers and police at a media conference links an activist named "Burin", who is already in jail waiting to be tried on lese majeste charges, to Patnaree Chankij and her son.

The charges against Ms Patnaree appear to be based on a series of Facebook messages sent to her by Burin.

It is not clear what all the messages say because they are blurred out in the graphic, but when the person writing the messages asks Ms Patnaree if it is OK to talk to her about these issues, she replies with a single word: "ja".

"Ja" can mean a non-committal "yes" but can also be used to acknowledge you're listening and to keep the conversation moving - much like an Australian might say, "yeah, right".

The police allege Ms Patnaree's lack of rebuttal amounts to approval and therefore breaches Article 112 of Thailand's Penal Code - defaming the King, Queen, heir apparent or Regent.

She has also been charged with a separate crime under the Computer Act.

Patnaree Chankij was granted bail on Sunday - Mother's Day - something quite unusual in lese majeste cases.

It is not clear how the police accessed the Facebook accounts of the people charged.

If found guilty, Patnaree Chankij will face between three and 15 years jail for each count of lese majeste.

It is not an empty threat - last year a man was sent to pre-trial detention for allegedly insulting the King's dog.

The stakes are high but lawyer Anon Nampha said he was confident.

"The evidence against her is so weak - all they have is the word "ja" [yes] to accuse her with... we can fight for this case," he said.