Vicki Dunne.

Vicki Dunne.

Legislative Assembly Speaker Vicki Dunne is looking increasingly isolated in her controversial push for a start-of-term religious ceremony, with the Clerk of the Assembly saying it would be too political for him to attend.

Other members of the Assembly's support staff said the planned ceremony had become ''divisive'' and were worried they would be seen to be ''picking sides'' if they attended.

It was likely the ceremony, planned for February 10, the day before the first sitting of 2013, could be attended by just by Mrs Dunne, her seven Canberra Liberal colleagues and their staff.

The idea received a further blow when the last Liberal to hold the office of Assembly Speaker weighed in to criticise Mrs Dunne's insistence on holding the service.

The ceremony, the first of its kind in the Assembly's history, was to be held at St Paul's Anglican Church in Manuka and proved controversial from the start.

Chief Minister Katy Gallagher made it clear she would not attend ''as a matter of principle'' and her seven Labor colleagues all backed their leader, refusing to go.

Balance-of-power Greens MLA Shane Rattenbury also said he had no intention of attending the multi-denominational ceremony and even accused Mrs Dunne of taking the Speaker's role backwards with the idea.

All politicians in the Assembly, their staffers and all of the building's support workers, who were supposed to be strictly non-partisan, received invitations to the service from the Speaker's office.

But Clerk Tom Duncan said the issue had become too politically charged and that attendance by himself or his secretariat staff might be seen as breaching their duties of impartiality.

Another non-executive staff member said the row between the Speaker and the Chief Minister had caused division in the building.

''It's become very divisive,'' the staff member said. ''Because it's all got political now, people are worried they will be seen to be taking sides, whether they go or they don't go.''

Mrs Dunne's office said it was not aware Mr Duncan had formally declined the invitation to attend the service and would not comment until confirmation was received.

Former Liberal Speaker Greg Cornwell, who held the post from 1995 to 2001, said he disagreed with Mrs Dunne's insistence on a religious ceremony.

''I would not have proposed a service,'' Mr Cornwell said.

''Religious affiliations or not are conscience matters like abortion or euthanasia and inevitably in a small legislature of 17, individual members will be singled out for not participating.''