NSW Labor has withdrawn bipartisan support for the relocation of Sydney's Powerhouse Museum to Parramatta.
Instead, Labor will propose a multi-purpose performance and cultural exhibition space at the Parramatta site and increased funding for arts and cultural activity, ongoing programs and infrastructure across Western Sydney.
The move comes after a NSW Greens motion for the release of documents on the relocation passed the upper house on Thursday with support from Liberal MP Matthew Mason-Cox who crossed the floor.
The motion will force the government to produce the business case for moving the museum to Parramatta at a projected cost of more than $1 billion.
Mr Mason-Cox, who has publicly criticised the coalition government's relocation plan, said his decision to cross the floor was "a matter of public conscience".
"I ask my party for their understanding in that regard," Mr Mason-Cox told parliament on Thursday.
Opposition Leader Luke Foley says the Berejiklian government's actions bear little resemblance to the original promise made by the former premier Mike Baird in February 2015.
He says the government is dismembering the Powerhouse - not moving it.
"I fear that Ms Berejiklian will announce a pale imitation of the original promise, which was an entire relocation of the Powerhouse Museum to Parramatta," Mr Foley said in a statement on Friday.
"Chopping the Powerhouse up into small pieces, strewn across Ultimo, Parramatta and Castle Hill, will deliver the worst of all worlds.
"Labor will not support the dismembering of the Powerhouse Museum. Either move it entirely to Western Sydney, or leave it where it is."