The NSW Berejiklian government has failed to hand over a business case for its controversial Powerhouse Museum relocation, two weeks after its own MP crossed the floor to force its release.

Liberal backbencher Matthew Mason-Cox went against his party two weeks ago to compel the government to release the documents.

But the government on Thursday claimed to have no preliminary or final business case, nor advice, relevant to the order to explain the move from Sydney’s Ultimo to Parramatta in the western suburbs.

The New Daily understands Labor, the Greens and the Shooters, Fishers and Farmers Party (SFF) will continue voting together to put pressure on the government when Parliament resumes next week.

Greens MLC David Shoebridge, who moved the order for papers earlier this month, told The New Daily the next move could include hitting the “nuclear button”.

Earlier this month he said that “dot points … summarised by a government keen to chop out inconvenient detail” would not be acceptable.

A spokesperson for Arts Minister Don Harwin told The New Daily the government was moving ahead with the relocation.

“It has been a thorough process and we will have more to say about this project in the near future.”

It’s understood the government will release a summary business case in an upcoming announcement.

SFF leader Robert Borsak – who is chair of a parliamentary inquiry into the relocation, with Mr Shoebridge as deputy chair – called on the government to come clean.

“When we’re hearing privately that the Powerhouse Museum relocation decision is before cabinet, it astounds me that there are no documents being produced by the government in response to the call for papers by the upper house,” Mr Borsak said.

“The government said they received a business case before December so they must have it or you have to call them liars.”

Former premier Mike Baird is expected to give evidence to the inquiry next month.

Labor’s shadow minister for the arts Walt Secord described the government as “arrogant and contemptuous”.

“Either this is a massive cover-up, or worse, there is no business case at all. This is another example of the Berejiklian government’s culture of cover-up and lack of transparency.”

The Greens motion, passed earlier this month with the support of Labor and SFF, called for “the preliminary and final business case for the relocation of the Powerhouse Museum from Ultimo to Parramatta”.

It also called for “any legal or other advice regarding the scope or validity of this order of the House created as a result of this order of the House”.

The Department of Premier and Cabinet, Premier Gladys Berejiklian’s office, Mr Harwin’s office, the Planning and Environment Department and Infrastructure NSW all said they had no such documents in their “possession, custody or control”.

Mr Shoebridge said the government was “getting to the point of farce”.

“This was an order of the Parliament and the Coalition government has again sought to avoid scrutiny this time alleging there is no preliminary or final business case to produce,” he said in a statement.

“This is now a test of democracy between an increasingly unaccountable executive government and the Parliament.”

Earlier on Thursday, an open letter arranged by the Sydney Business Chamber urged Ms Berejiklian and Opposition Leader Luke Foley to continue with the project. It was signed by more than 30 organisations based in Western Sydney.

The fiercest opponents of the relocation – in the Greens and SFF – want to build Western Sydney a dedicated culture centre at a different site in Parramatta, instead of moving the Powerhouse.

That dedicated centre would respond to the area’s “unique Aboriginal, colonial, and migrant history”, Mr Shoebridge told The New Daily earlier this month.

The parliamentary inquiry put the cost of the relocation at $1.5 billion, and heard the government’s proposed site is flood prone.