Prime Minister Malcolm Turnbull may be forced to water down draft laws to restore the building industry watchdog to get it through parliament.
The legislation that triggered the July 2 double-dissolution election has already passed the lower house and is scheduled for debate in the Senate on Tuesday.
But it's not clear whether the government has the numbers, with crossbenchers keeping their cards close to their chest.
Independent Senator Derryn Hinch said things were "moving along" following meetings with Employment Minister Michaelia Cash, Opposition Leader Bill Shorten and the construction union.
He, along with Nick Xenophon, are working on some amendments that take into account apprentices, subcontractors and commissioner accountability.
"The government's going to have to accept some amendments," he told ABC radio on Thursday.
"Whether or not the numbers are there to pass the bill eventually, I'm not sure. If indeed it does get through, it'll be a more polished and leaner machine than the government originally came up with, which caused the double dissolution."
He labelled himself pro-worker but anti-corruption, and hopes the government wants to find a middle ground just as much as he does.
"I don't see this as a union-busting exercise and neither should it be."
Mr Turnbull has remained coy on whether he thinks the bill will passed.
Asked about it in Sydney on Thursday, the prime minister said: "We look forward to the support of the Senate for this very important legislation."
Deputy Labor leader Tanya Plibersek said Labor was working hard to stop the legislation clearing parliament.
"We know that last time we had an ABCC, productivity on building sites went down and deaths on building sites went up," she told reporters.