For the group calling itself the Concerned Citizens of Canberra, potentially quite a bit.

The vocal objectors to the proposed Gungahlin mosque are facing an existential crisis in the ACT Supreme Court.

The group took legal action against the project in August this year, initially challenging the government's refusal to extend a public comment period.

And the court heard this morning their case now included a challenge to "the substantive decision itself".

But they're facing a substantial legal hurdle.

Master David Harper this morning warned the case was at risk of being thrown out because it was first lodged in the name of a group which didn't legally exist.

The papers were first filed on August 9 in the name of "Concerned Citizens of Canberra".

But the group only became formally incorporated – becoming "Concerned Citizens of Canberra Inc" - four days later after lawyers for the ACT government pointed out they didn't technically exist.

Master Harper said case law seemed to suggest the proceedings should be discontinued.

"The authorities say if you commence proceedings in the name of an entity which doesn't exist then the proceedings are nullified," he said.

"It mightn't be the end of it, you may come to the view that there's a way around it, and convince the court."

"But prima facie it looks to me, and the authorities would lean towards, the entire proceedings being a nullity."

If the proceedings were discontinued the group might be able to re-lodge their claim under their incorporated name.

But such a move might fall foul of time limits imposed on bringing legal action.

The group delivered thousands of flyers to Gungahlin homes in June, urging residents to oppose the mosque because of its "social impact", "public interest" and concerns about traffic and noise.

The public notification period for the development closed on July 6, with the ACT Planning and Land Authority receiving more than 50 submissions.

The Concerned Citizens of Canberra asked for the window to be reopened but were knocked back on August 6.

They then went to court saying the refusal was "likely to result in a denial of natural justice".

They claim the planning authority's decision not to extend the comment period was an "improper exercise" of their power.

The group has waged a concerted campaign against the mosque.

The secretive participants in the campaign consistently told media and government that they were concerned with local planning issues, including traffic and noise.

But The Canberra Times revealed in June that Irwin Ross, the group's spokesman, was a Christian fundamentalist activist who lived at least 15 kilometres from the proposed Valley Avenue site.

And the solicitor who lodged the claim on the group's behalf, Robert Balzola, was engaged in at least two similar campaigns in Sydney.

Lawyers for the Chief Planning Executive, the named defendants, have applied to have the case struck out altogether.

The case will return to court at a later date.