The Federal Opposition has formally requested access to secret volumes of the Royal Commission into Trade Union Governance and Corruption's findings.

Key points: Labor calls for access to 'secret' findings handed down last year

Labor calls for access to 'secret' findings handed down last year Material may be shown to Senate crossbenchers

Material may be shown to Senate crossbenchers Parliament will hear plan to bring back construction commission in February

The Government has decided to show the full findings to key Senate crossbenchers, whose support is needed to pass any legislation to help it crack down in union corruption.

The plan has incensed Labor, which argues it is another example of the Government using the commission for political gain.

In a letter obtained by the ABC, Opposition employment spokesman Brendan O'Connor wrote to Employment Minister Michaelia Cash asking for the Opposition to also be afforded the opportunity to read the secret volumes of the report.

"I do note that if you are to provide access to the reports your Government is ignoring the insistence of its own royal commissioner Dyson Heydon that these volumes should remain confidential," Mr O'Connor wrote.

"The obvious question arises, why does the Abbott-Turnbull government disagree with its own royal commissioner?

"It appears the Government only respects the royal commission's findings when it suits your immediate political interests."

Mr O'Connor said such an attitude would be confirmed if the Government failed to give the Opposition access to the confidential volumes.

"If your Government wants to rely on these secret volumes to make the case for legislation, the Opposition is of the strong belief that the Government must, at a minimum, provide them to all sides of the Parliament, and potentially to other interested parties," Mr O'Connor wrote.

"I ask, therefore, if the reports are to be provided to crossbench senators that the Opposition be afforded the same opportunity."

Seven volumes of findings were released publicly at the end of last year, after two years of public hearings examining the conduct of the trade union movement across the country.

However some of the findings have been held back to protect witnesses.

Legislation to be introduced next month

Upon releasing Mr Heydon's findings, Prime Minister Malcolm Turnbull said he wanted to bring back the Australian Building and Construction Commission (ABCC).

This article contains content that is not yet available here.

The legislation, previously blocked in the Senate in August, will be reintroduced when Parliament resumes in February.

Without the support of Labor or the Greens, the Government needs six of the eight crossbenchers' support to pass any legislation.

Senator Cash stopped short of calling for a double dissolution election if it is rejected for a second time.

But she vowed to fight for the changes when Parliament resumes.

Tasmanian independent senator Jacqui Lambie is campaigning for a private viewing of the findings.

"As a Tasmanian senator, I need all the royal commission information, 100 per cent not 75 cent — to make fully informed decisions about critical legislation before the Senate," Senator Lambie said.

"Not even a royal commissioner should be able to prevent an Australian senator from carrying out their duties in a free and fair manner."

Senator Lambie argued there was precedent for such reports being shown to senators.

Fellow independent senator Glenn Lazarus has already suggested he is not in favour of measures such as reintroducing the ABCC, but told the ABC that he would like to see the report.

"Like any piece of legislation, I like to see the full facts and the full, get right over the issue, and this will certainly help do that," the Queensland senator said.

"Whether or not that sways my vote, we'll have to wait and see."