Two men who claimed their Islamic-influenced group was not subject to Australian law because it was a "basic religious charity" have been found to have illegally cleared a rural property north-west of Sydney by the NSW Land and Environment court.

The Hawkesbury City Council launched civil action against Dr Mustapha Kara-Ali and Diaa Kara-Ali for clearing trees and developing a block of land at Colo, without seeking development approvals.

The two men did not attend the hearing.

Justice Terence Sheahan handed down his judgement on the case in the New South Wales Land and Environment Court on Monday afternoon, where he found the land clearing, and associated development, was carried out illegally.

Before and after photos show the loss of vegetation on the block. ( Supplied )

"I've come to the conclusion the respondents are in no way exempt by their charity status from the planning law," Justice Sheahan said.

Mustapha Kara-Ali, a former member of then-prime minister John Howard's Muslim Community Reference Group, and past postdoctoral fellow at Harvard University, heads a religious guild he founded called Diwan Al Dawla — which operates and holds prayers out of the Colo property.

Illegal structures must come down, judge says

Judge Sheahan ordered that some structures on the land, including a gate entrance, fencing, flag poles, concretes slabs and structures, be demolished and removed within 28 days.

He further ordered that two dwellings and a septic tank be removed within 14 days, and that the Kara-Alis pay the costs of the Hawkesbury City Council.

Judge Sheahan also ordered the land could not be used for religious worship until proper permits had been approved.

"The respondents … are restrained from using … the land … for the carrying out of any and all religious activities and devotion, self-discipline, ritual baptism, inter-community prayers, contemplation and religious study or for the purposes of public worship … until development consent has been granted," he said.

Within 42 days, the pair are required to submit to the council plans on how they will restore and rehabilitate the property.

Sorry, this video has expired Men in Islamic guild accused of illegal land clearing skipped court to build shed

The ABC contacted Mustapha Kara-Ali for comment.

In a previous interview with the ABC, Dr Kara-Ali claimed the Hawkesbury City Council was infringing on his group's religious freedom by pursing him over the illegal clearing.

"Diwan Al Dawla, as a basic religious charity, is not required to comply with Australian laws," he previously wrote in a letter to the Hawkesbury City Council.