Malcolm Turnbull has made workplace law changes a priority for the second-last sitting week of parliament for the year.
The prime minister used the bills, which will restore the building industry watchdog and put in place a new regime for tackling union misconduct, as the triggers for July's double dissolution election.
The Senate program for next week confirmed the first piece of business on Monday would be the bill to set up the Registered Organisations Commission (ROC).
The Australian Building and Construction Commission legislation is set down for Tuesday.
With the Greens and Labor opposed to the bills, and Family First's Bob Day having quit the upper house to deal with his housing business collapse, the government will need the support of eight crossbenchers.
Employment Minister Michaelia Cash declined to say on Wednesday how confident she was in securing enough support, but talked up the benefits of the ROC.
"With annual revenue of $1.5 billion, assets of $2.5 billion, plus tax exempt status, registered organisations should be accountable and transparent," she said.
"The two million Australians who entrust their money to their union or employer group deserve to know that it is being run honestly and in their best interests."
One Nation's four senators are expected to support the bills, although Western Australia's Rod Culleton could be preoccupied with a court challenge to the validity of his election which has a directions hearing on Monday.
If the government can secure the votes of the Nick Xenophon Team's three senators it will then only need one more vote from the Liberal Democrats' David Leyonhjelm, or independents Derryn Hinch or Jacqui Lambie.
Senator Lambie has stated she will oppose the bills which she said had "more holes than a shooting range".
If the bills fail, Mr Turnbull has the option - following his election win - to bring both houses together for a rare joint sitting of parliament to pass them.
The ROC will regulate unions and employer organisations using similar investigative powers to the Australian Securities and Investments Commission and having the option of seeking penalties of up to five years in jail plus $360,000 in fines.