The Greens have rejected a federal government offer to look at a confidential volume of the royal commission into trade union corruption.

Employment Minister Michaelia Cash last week told the minor party, which holds key votes in the Senate to pass new building watchdog laws, it could not see the volume.

But the minister on Monday night wrote to the Greens saying one of its parliamentarians could look at the volume so long as he or she did not disclose its contents to any other person, did not take notes and viewed it in the presence of a Department of Prime Minister and Cabinet officer.

Greens MP Adam Bandt said the conditions were a "desperate attempt" by the coalition government to win the party over.

"If the government thinks this is so important, let all members of parliament and all senators see this document, debate it and discuss it," he told reporters in Canberra on Tuesday.

"Transparency is to this government what sunlight is to a vampire."

The government will have to win over six of the eight crossbenchers in order to pass the bill reinstating the Australian Building and Construction Commission, which will be reintroduced to parliament on Tuesday.

It has agreed to provide four crossbench senators with an unedited version of the secret volume.

So far, only two of them - Family First senator Bob Day and Liberal Democrat David Leyonhjelm - have indicated they will vote with the government.

Senator Leyonhjelm said the government was making a mistake allowing access to the volume because the reason it was secret was to protect witnesses and not compromise a fair trial.

Independent senator Nick Xenophon echoed those concerns and described the secret report as a "red herring".

Fellow independent John Madigan hit out at the government's "glowing inconsistency and Chinese whispers".

Senator Cash said it was all about getting "good policy" through the parliament.

Opposition Leader Bill Shorten described the government's handling of the royal commission's report as a circus.

"The way this government is playing these reforms, it smells more of politics than policy," he said.

The royal commissioner who initially recommended creation of the ABCC in 2001, following his investigation into the building industry, has warned there is a huge economic cost if it isn't revived.

Terence Cole said the reduction in unlawful action was worth $6.3 billion in 2012.

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 workplaces laws," she said.

The Master Builders Association urged crossbenchers to pass the legislation, saying the industry had an "institutionalised culture of unlawfulness".

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