The Government is one step closer to passing the final piece of its industrial relations legislation after agreeing on a deal with Liberal Democrat senator David Leyonhjelm.

Key points: "Subject to a few relatively small details, we're there," David Leyonhjelm says

"Subject to a few relatively small details, we're there," David Leyonhjelm says Government has agreed to accept amendment which removes reverse onus of proof, he said

Government has agreed to accept amendment which removes reverse onus of proof, he said Nick Xenophon Team's three senate votes are not yet secured

Senator Leyonhjelm revealed the agreement on AM this morning.

"Subject to a few relatively small details, we're there," he told the program.

A formal announcement is likely later today with full details to be revealed.

But Senator Leyonhjelm revealed on AM the Government had agreed to one of his demands.

"The Government has agreed to accept an amendment which removes reverse onus on proof, so that's good they will accept my amendment on that," he said.

Dropping reverse onus of proof effectively raises the standard of evidence required to prove criminality on building sites.

The legislation aims to restore the Australian Building and Construction Commission (ABCC), designed to police illegality in the construction industry and branded by Labor as anti-union.

The bill is not certain to pass this week, with the Nick Xenophon Team's three senate votes not yet secured.

The ABC understands a gruelling four-hour meeting between Senator Xenophon, Employment Minister Michaelia Cash and her staff made little progress.

It is understood Senator Xenophon's demand for security-of-payment protections for building subcontractors was a sticking point that is raising complex constitutional questions.

With Parliament rising at the end of the week, passing the bill in coming days would give Prime Minister Malcolm Turnbull a triumphant end to the year.

The previous senate blocked former prime minister Tony Abbott's attempts to pass the legislation.

The ABCC bill was a trigger for Mr Turnbull's high-risk double-dissolution election strategy — a strategy that a win on the bill this week would justify.

Senator Leyonhjelm was one who doubted the strategy when the election delivered a bigger and potentially unwieldy crossbench.

The Government has always argued the new crossbench was more workable than the last.

"I must admit I didn't believe it when the Government said that," Senator Leyonhjelm told AM.

"Perhaps I was wrong. Who knows, it's early days."