He's a highly regarded paediatrician but the suffering he saw on Nauru left him with nightmares. But as of next month Professor David Isaacs could face two years jail if he speaks out about it.

In May the Border Force Act quietly passed both houses of parliament and became law.

Now teachers, doctors and security staff could be subject to two years jail if they speak publicly about what they witnessed.

"It's all very vague it's all very secretive, it's frightening I think," Professor David Isaacs said.

"It's the sort of thing you might have expected in a very right wing, almost fascist country, certainly not our so-called democratic country.

"So now it says that if I see a child that's in danger or that's seriously ill because of the conditions there and their mental health is really bad, even if I come back to Australia and talk about it in to the media, even put it on Facebook, I could face two years in prison. That's appalling."

David Isaacs runs a clinic for refugees in Sydney's western suburbs.

He was invited by the government to work in the offshore detention centre in Nauru in December.

The island is home to just 10,000 Nauruans.

The detention centre is in the least hospitable part of the island, near the old phosphate mines that once sustained Nauru's economy.

"People live in the most appalling conditions in tents which are adjacent to each other so there's no secrecy," he said.

"There's 100 metres to the nearest toilet facilities and no water in the tents so sometimes people won't even go across the open ground at night because they're scared of being sexually assaulted by the guards, which has happened."

For days after returning from Nauru, both Dr Isaacs and the nurse who accompanied him had Kafka-esque nightmares.

He said the suffering of children he treated was the hardest to reconcile.

"I saw a six-year-old child who tried to hang herself with a fence tie," he said.

"I saw a 15-year-old brave lad who'd sewed his lips up and his parents were cross with him for doing it, and he was cross with them because when he collapsed they let the medical staff cut the ties on his lips," he recalled.

"I just saw endless trauma ... I saw 20 or 30 children and the trauma they were going through, over a year in prison really without knowing what their fate was going to be, it was appalling."

Saturday June 20 is World Refugee Day.

Dr Isaacs is one of several speakers at the Lismore Workers Club at 7.30pm, a guest of the Alstonville Justice Group.

He said it will be one of the last occasions when he'll be able to speak freely without fear of prosecution.

"(Prominent QC) Julian Burnside AO said that until July 1st I'm safe; from July the first it's not clear what would happen if I would mention what happened previously on Nauru, so from July the first I've got to be careful."

However this professor of paediatrics from the Westmead Children's Hospital said he now feels he has a duty.

"Advocacy is about speaking up for people with no voice and I have not been a good enough advocate before and I've decided it was time I was," he said.

Dr Isaacs said despite the position of both major parties, he believes many ordinary people do care about Australia's treatment of asylum seekers in offshore centres.

"This is deliberate, we're spending half-a-million dollars per person per year but it is to punish them, it's essentially a punitive deterrent effect," he said.

"Tony Abbott and even the Opposition are acting as if asylum seekers are the baddies, it's ridiculous. These are people fleeing from persecution, they need our sympathy not our punishment.

"The Italians had a day of mourning when a boat load of Liberian refugees sank off the Italian coast. They treat them as human beings and we don't."