The federal government has u-turned on giving Labor and the Greens access to secret volumes of the trade union royal commission report.

The government hopes the report will bolster its case for re-establishing the controversial building watchdog – the Australian Building and Construction Commission – and Employment Minister Michaelia Cash maintains the change of heart is about getting good policy through the Senate.

“We will give access to the confidential volumes to one member of the Australian Labor Party and one member of the Greens,” she told the ABC.

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Meanwhile, the Howard government royal commissioner Terence Cole, who recommended the ABCC be set up in 2001 following his investigation into the building industry, has warned there is a huge economic cost if it isn’t revived.

In a letter to The Australian, he said in 2012 the reduction in unlawful action was worth $6.3 billion per year.

“Surely it is incumbent upon those who oppose the reintroduction of the ABCC to explain how it is to the advantage of the economy, and to the Australian people who bear the great costs of unlawful action, to have an increased level of unlawfulness in the building and construction industry which the ABCC has demonstrated it can suppress, but which existing arrangements do not,” he wrote.

It is a sentiment shared by Senator Cash, who says the sector has been singled out.

“This is a unique sector in Australia that fails to comply with their workplace’s laws,” she told ABC radio.

Senator Cash defended her handling of the legislation, saying some of the crossbenchers were waiting for the report to be made available before making their decision.