The Turnbull government has shut the door to anything but minor changes to laws restoring the building industry watchdog.
Parliament will return on April 18 to reconsider a bill to restore the Australian Building and Construction Commission.
If the Senate rejects it, a double-dissolution election will be held on July 2 and the two houses brought back for a joint sitting to pass it.
The government will need six out of eight crossbench senators to pass the bill, but most of them are demanding the ABCC be replaced by a national anti-corruption commission.
Employment Minister Michaelia Cash says she will negotiate in good faith but would not accept anything that fundamentally changed the bill, such as a national ICAC.
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"That is not something the government is prepared to do," she told ABC radio on Thursday.
She said "most" of the amendments brought forward by the crossbenchers to date were fundamental changes.
Any amendments that came forward in coming weeks would need to be agreed by the whole crossbench to be seriously considered.
Independent senator Jacqui Lambie told AAP there was a growing consensus on the crossbench around the need for a federal ICAC.
"I think (Palmer United Party senator) Dio Wang's right on to it. We want a national ICAC, that's what we're calling for ... we want a watchdog over everything, not just a minority of it," Senator Lambie said.
She said work was progressing on another amendment around protecting the right to silence.
Opposition Leader Bill Shorten said the government was engaged in an anti-union campaign and there were better ways to improve the system, including making use of the Australian Securities and Investments Commission.
"The problem with the Liberal party under Mr Turnbull or Mr Abbott is that they always overreach," he said.
