Council workers visiting a rural property in Sydney's north-west used by a religious group were told police needed the riot squad and a Polair helicopter when accompanying them due to safety concerns, a court has heard.

Hawkesbury City Council has launched civil action against Dr Mustapha Kara-Ali and Diaa Kara-Ali in the Land and Environment Court, alleging the men carried out illegal land clearing, earthworks and built gates, fences and driveways without seeking any of the relevant development approvals at a property in Colo, in Sydney's north west.

Mustapha Kara-Ali, a former member of then-prime minister John Howard's Muslim Community Reference Group and past postdoctoral fellow at Harvard University, is the Imam of religious guild Diwan Al Dawla, which he founded.

In a letter by Dr Kara-Ali to council staff, tendered in the court documents, he said the members of his guild live "separated from secular lifestyles to pursue a religious mode of worship and an ascetic lifestyle under an oath of self-sacrifice and dedication to the purposes of Diwan Al Dawla".

The letter said the Colo property was used "for the carrying out of religious activities of devotion, self-discipline, ritual baptism, inter-community prayers, contemplation and religious study".

The property is used for religious activities of devotion, ritual baptism and prayer, according to the group's Imam, Dr Mustapha Kara-Ali. ( Supplied: NSW Courts )

The matter was set down for a two-day hearing starting today, but neither of the men attended court and there was no lawyer there to represent them.

The hearing has continued without them and it is alleged development on the site has continued despite the court proceedings and repeated requests from council for them to stop.

Lawyer for the council, Mark Cottom, told the court a council officer had requested police accompany them on a site inspection of the property, because they might have required forced entry.

"The police appear to have significant concerns in relation to safety … wishing to have the riot squad and Polair available," Mr Cottom said.

'Illegal' barn, shed and homes on the site

Mr Cottom tendered evidence that council officers had seen construction of a barn and shed had begun on the property.

He also tendered photos of two manufactured homes that have allegedly been moved onto the site.

The court heard earlier this month a council worker, Gary Collins, went to the property where he saw a number of flag poles had been installed and were flying flags that appeared to be for Diwan Al Dawla and Southern Chariot Stud.

Mr Collins approached two men who were moving earth and building a shed at the site and was told by one of them that he was building the shed, as instructed by Mustapha and Diaa Kara-Ali.

According to Mr Collins's affidavit, when told about the issues with the site, the builder replied, "Now I know why they were hassling me and in such a rush to get the shed up".

In evidence to the court, Mr Collins said he had visited the property in the past week and saw people measuring a concrete slab and some metal framework on top of the slab.

In correspondence with the council, tendered to court, Dr Kara-Ali claimed his organisation was exempt from Australian law because it was classed as a basic religious charity.

However, this claim is not supported by the Australian Charities and Not-for-profits Commission.