The government appears set to secure Senate support this week for tough legislation to crack down on bad behaviour in the union movement, after the near finalisation of an agreement with Centre Alliance for several significant changes.

The bill deals with officials and unions that consistently break existing laws – the federal court could disqualify the person from holding office or deregister the union or a branch of it.

The legislation – which has its origin in the royal commission into trade union behaviour - also proposes a public interest test for amalgamations of unions.

Centre Alliance has sought changes to raise the threshold for disqualifications and deregistrations. These include

• inserting a system of demerit points as a threshold for applications, so unions or officials would not be acted against for minor infringements. An official or union would have to reach a minimum penalty threshold over the preceding decade

For an individual, that would be 180 penalty points over 10 years for a breach of various laws or contempt of court in relation to these laws. A union would have to reach 900 penalty points over 10 years before it could be considered.

• the power to apply to the federal court for deregistration or disqualification to rest only with the Registered Organisations Commissioner, not with the minister or interested parties

This would make the process more independent. It would bring the change into line with the Corporations Act, where only the Australian Securities and Investments Commission can move for disqualification of directors.

• ensuring that the federal court could only deregister a union or disqualify an official for grave misconduct. The court would also consider whether a public interest element provided exonerating circumstances.

In another change proposed by Centre Alliance, the public interest test for unions mergers would only be triggered where one or both organisations had a history of misconduct. The threshold would be that a union had a substantial number of compliance events over 10 years.

The government will need three votes out of those held by Centre Alliance (with two senators), One Nation (also two) and Jacqui Lambie.

Centre Alliance’s Rex Patrick said on Sunday the party was “close” to final agreement with the government. It had been working constructively with industrial relations minister Christian Porter who had been “obliging”.

The bill in its original form was a “sledge hammer to crack a nut when what was needed was a nut cracker,” Patrick said.

Lambie has previously said she will vote for the bill unless militant construction union official John Setka resigns his union positions, which he has refused to do.

Porter said “the drafting of amendments to reach a working compromise is advanced”.

“Despite Labor and the ACTU’s increasingly hysterical and farcical claims about this bill, it does not stop anyone from joining a union, nor does the bill have any impact whatsoever on a union’s ability to exercise its rights to represent its members, including in relation to underpayment of wages and health and safety concerns.

"Labor or CFMMEU assertions to the contrary are completely and utterly false,” Porter said.

Although the legislation is aimed at unions, the government points out it also covers employer organisations.

Opposition leader Anthony Albanese told the ABC the legislation was “just about attacking unions” and “can’t be fixed”.

“This is an attack on the organisations that go into workplaces that deal with issues like wage theft, that ensure that there’s proper occupational health and safety … They ensure that you don’t have worker exploitation, including foreign workers on work sites. Unions play a critical role in civil society”.

He said the legislation was “an attack on the fundamental right of people to belong to unions.”

“This government hasn’t changed its spots from WorkChoices. They essentially don’t believe in unions’ right to exist, and that’s what the legislation is about. It’s bad legislation. It is unsupportable in my view and we won’t be voting for it,” Albanese said.

Mandatory minimum sentences also a headache for Labor

Labor faces a wedge on another piece of legislation – a bill to impose mandatory minimum sentences for child sex crimes under Commonwealth law. The ALP opposes the mandatory sentencing aspects.

Porter, who is also attorney general, said about 39% of all child sex offenders convicted of Commonwealth offences didn’t spend any time in prison.

“The Morrison government believes that is simply not good enough, which is why we have proposed mandatory minimum jail terms to ensure the punishment fits the crime.”

Molan to fill Senate vacancy

Former Liberal senator Jim Molan, who lost his seat at the election, was chosen on Sunday to fill the casual Senate vacancy created by the departure of Arthur Sinodinos, who is to become ambassador to the United States. Molan defeated several candidates, despite criticism of him from some Liberals for running a campaign at the election urging people to vote for him “below the line” rather than casting an above the line vote for the official Liberal ticket.

Michelle Grattan does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.