The family of an Australian man jailed for murder in Bulgaria holds fears for his safety after the 32-year-old stopped eating three weeks ago in a prison hunger strike.

Key points: Palfreeman started Bulgaria's first convicted prisoners' union to expose corruption and abuse

Palfreeman started Bulgaria's first convicted prisoners' union to expose corruption and abuse Family calling for Palfreeman to be returned to Australia via parole or government intervention

Family calling for Palfreeman to be returned to Australia via parole or government intervention Palfreeman is halfway through his 20-year sentence

Jock Palfreeman is serving a 20-year sentence for stabbing and killing 20-year-old law student Andrei Monov during a melee in Bulgaria's capital, Sofia, in late December 2007.

The Australian stopped eating on April 21 to protest what he claimed was unfair treatment by prison authorities and the Bulgarian Government in response to his human rights work while behind bars.

This week Palfreeman was moved from Kazichene low-security prison to the hospital at the Sofia Central high-security prison.

Jock Palfreeman helped set up a prisoner union with other inmates. ( Australian Story: Belinda Hawkins )

His father, Dr Simon Palfreeman, is trying to convince the Bulgarian authorities to let him see Jock.

"My fear is that the time is now approaching when starvation could cause permanent damage," Dr Palfreeman said.

Simon Palfreeman stands outside the Bulgarian prison in which his son, Jock, has spent more than 10 years behind bars for murder. ( Australian Story: Belinda Hawkins )

Palfreeman's 86-year-old grandfather Tony, who will travel to Sofia later this month, said the family was "greatly concerned about Jock's emotional and physical wellbeing".

"He has been through enough already and we ask that he be returned to Australia either by parole or by government intervention," Mr Palfreeman said.

Palfreeman has always claimed he drew the knife in self-defence after a group of young, drunk men turned on him when he tried to stop them assaulting a Gypsy.

A still from CCTV showing the events that unfolded the night that Bulgarian man Andrei Monov was stabbed. ( Australian Story: Belinda Hawkins )

Since his conviction in 2009, Palfreeman has advocated for changes to Bulgaria's prison system.

Seven years ago, he established Bulgaria's first convicted prisoners' union, the Bulgarian Prisoners' Rehabilitation Association (BPRA), which has drawn attention to examples of corruption within the prison system and of abuse.

Andrei Monov (left) died from a single stab wound to the side of his chest. ( Supplied )

The association has also helped prisoners to take cases of alleged injustice to Bulgarian and European courts, earning it accolades from human rights groups but opposition from Bulgaria's prison authorities.

High-profile lawyer Geoffrey Robertson QC has called on the Australian Government to make "immediate representations" on Palfreeman's behalf.

"It is urgently necessary to stop the discrimination against him so that he can break his hunger strike," Mr Robertson said.

"He is a human rights hero being made to suffer extreme privations because of his good work."

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 1 minute 11 seconds 1 m 11 s Jock Palfreeman in a never-before-seen 2015 interview with Australian Story.

Celebrities back Palfreeman's cause

Mr Robertson is not the only high-profile Australian to take up Palfreeman's case.

Australian film director Rachel Ward, who has visited Palfreeman twice in jail, most recently a fortnight ago, told Australian Story she believed he had been "persecuted for telling the truth about prison conditions".

Ms Ward, Mr Robertson and other well-known Australians, including Cate Blanchett, Bryan Brown and Simon Baker, are now petitioning Bulgaria's Justice Minister.

"Our government has dropped the ball and the Bulgarians need to know [we] want to see Jock's case moved forward," Ward said.

Rachel Ward (centre) waiting last month outside Kazichene low-security prison to visit Jock Palfreeman. ( Supplied )

In April last year, Palfreeman withdrew a parole application fearing it was not possible to receive a fair hearing.

It came after his victim's father organised a protest outside the Sofia Palace of Justice and issued a veiled threat on television, warning he had not forgotten "the skills" he learnt in the military.

In another incident last year, Palfreeman was slapped with three disciplinary punishments in quick succession shortly after he submitted an opinion on behalf of the BPRA to the Committee of Ministers of the Council of Europe on the execution of a judgment of the European Court of Human Rights (ECHR).

The judgement condemned Bulgaria for inhuman and degrading conditions in several of its prisons.

Jock Palfreeman arrives at court in 2010 during his unsuccessful appeal. ( Supplied: Dobrin Kashavelov )

Bulgarian human rights advocate, Dr Krassimir Kanev, who worked with the BPRA on a working group established to address the European concerns, said "there was broad-ranging reform needed" and Palfreeman's report was "embarrassing for the Government".

Bulgarian human rights advocate Krassimir Kanev. ( Supplied: Dobrin Kashavelov )

Palfreeman was accused of inciting civil disobedience by distributing BPRA stickers, having soft porn on the computer he shared with other prisoners, and failing to follow a guard's orders during a search of his prison cell. The punishments further hurt Palfreeman's chances of parole.

"Until then he had an excellent record," Dr Kanev said. "So clearly they've taken revenge."

Dr Palfreeman said the Department of Foreign Affairs and Trade (DFAT) had failed to take up his son's concerns with the Bulgarian Government, despite repeated requests.

"It's getting out of hand given the seriousness of the ongoing hunger strike that they aren't pulling out all stops," he said.

In a statement, DFAT said Jock Palfreeman was receiving high-level consular assistance including "consular officials closely following his legal process, representations to the Bulgarian Government on his case, regularly visiting him in prison to monitor his welfare, and communicating with his family in Australia".

Australian Story has contacted the Bulgarian Justice Minister and his deputy for a response.