Canberra community arts group Megalo had been due to move into the historic space next to the old Bus Depot and Glassworks as early as next winter.

But the Greens and the Canberra Liberals joined forces on the floor of the Assembly yesterday to send the Government's decision to a Legislative Assembly committee, a process that is set to take up to six months.

Planning authorities are considering a development application that would allow $3.9million of work to the heritage-listed shed before the planned takeover by Megalo.

After a concerted lobbying campaign by Canberra's choral music community, which wants to use the workshops to stage concerts, Canberra Liberals arts spokeswoman Vickie Dunne and her Greens counterpart Caroline Le Couteur pushed through a motion yesterday referring the Megalo deal to committee. Both women said there was a lack of process in the decision to lease the building to Megalo and that the Standing Committee on Education, Training and Youth Affairs would examine the choral music community's claims.

Megalo chief executive Alison Alder could not hide her disappointment yesterday, saying the Assembly's decision would send her group's planning into turmoil.

''Megalo has acted in good faith throughout the three-year process of consultation, scoping and negotiation with the ACT Government,'' Ms Alder said. ''Further to that point, Megalo believes that the ACT Greens should act in good faith in light of passing the capital works budget earlier this year.

''Megalo feels, rightly, that its interests are not being considered and that it is being used as a political punching bag.''

Arts Minister Joy Burch said the two other political parties had combined to ''trample'' Megalo.

''We've seen the ACT Liberals and the ACT Greens come together and absolutely trample all over Megalo, which is a solid community arts organisation,'' the minister said.

''What they have done is colluded and had a devastating impact on this arts organisation, which will see their processes and their practices and their business all on hold for some time to come.''

But Mrs Dunne said the Government had never had an expert report on the much-vaunted acoustics of the workshop building, the characteristic that made it such a prized asset for the choral community.

''There are serious questions about the quality of the acoustics and I'm not prepared to let this Government vandalise what could be a very important acoustic place because they haven't done the work,'' Mrs Dunne said.

''We're looking for a win-win for the music makers and the print makers at Kingston.''

Ms Le Couteur said the Liberals and the Greens were moving to make up for Government failings.

''The Government has failed to fully evaluate the value of the Fitters' Workshop to choral and other classical music groups, which has left a huge question hanging,'' she said.

ANU Choral Society, which has led the campaign for music in the shed, could not be contacted for comment yesterday.