An Australian father accused of training pilots for the Chinese military has been transferred to a maximum-security NSW jail without explanation, his supporters say.

Daniel Duggan, a 54-year-old former US marine and naturalised Australian citizen, was arrested by Australian authorities last year under an agreement with the US government, which has accused him of illegally assisting the Chinese state

Duggan, who denies the charges, is due to face a Sydney court on Monday as he fights extradition.

That appearance comes a week after he was moved from Silverwater remand centre to Lithgow’s maximum security prison.

A spokesman for Duggan told AAP the facility, mainly housing convicted prisoners, has very few provisions for meetings with his legal team.

“A 45-minute meeting in the facility’s single video conference room with his legal team this week, ahead of Monday’s court appearance, was interrupted with technical issues every three minutes, to the point it was impossible to follow the conversation or discuss legal strategy,” the spokesman said.

“No additional time was provided.”

The Duggan family is unable to access legal aid and has launched a crowdfunding campaign for his defence.

The former US Marine, through the spokesman, said the case was “a test of Australian sovereignty but is being fought by a struggling farming family in regional NSW, at great personal and financial expense”.

Mr Duggan’s supporters had previously raised issues with the conditions in Silverwater.

A complaint was filed in February to the United Nations on the basis his ongoing custodial conditions constitute a violation of the International Covenant on Civil and Political Rights, by failing to protect him from inhumane or degrading treatment and not segregating him from convicted prisoners.

Corrective Services NSW said it did not comment on the status of individual inmates.

It has previously said it took great care to determine appropriate security classifications and placements for inmates.

“Inmate and staff wellbeing is a top priority in NSW correctional centres,” a spokeswoman told AAP last month.

Prisoners were classified according to security classification levels set out in the relevant regulations, she said.

The matter of Mr Duggan’s eligibility for extradition will come before a Sydney magistrate on Monday, but the decision will ultimately be made by Attorney-General Mark Dreyfus.

-AAP