Labor is demanding to see proposed changes to union-busting legislation, warning a new demerit point system could be used to dole out heavy-handed punishments, for minor issues.
Opposition industrial relations spokesman Tony Burke has called for the Morrison government to release amendments, thrashed out with Centre Alliance, to a bill making it easier to deregister unions and ban officials.
"If they had nothing to hide this would be public already," he told ABC Radio National on Monday.
Under the demerit system, an official with 180 demerit points could be banned, while a union could face deregistration if it racked up 900 points.
Unions have pointed to lodging late paperwork, including financial records and membership registers, as examples of 500-point breaches.
Mr Burke said the nurses' union could also be deregistered for taking industrial action over staff-to-patient ratios.
"This is about at the very least, constantly tying up unions in paperwork, and realistically deregistering a large number of organisations and officials from being able to defend workers," he said.
Centre Alliance senator Rex Patrick insists unions and officials won't be pinged for minor misdemeanours.
But Mr Burke argues there's no way to be sure unless the government releases the details of its amendments before the bill comes before the Senate in the final sitting fortnight, which starts next week.
"These amendments cannot continue to be kept secret. The Australian people do have a right to know what is being planned," he said.
"If paperwork breaches are going to result in the deregistration of an entire organisation, we have a right to know that."
Attorney-General Christian Porter has rejected Labor and unions' concerns about the laws being used to launch deregistration over minor paperwork offences, saying the suggestion is "absolute nonsense".
The government needs four of six crossbench votes to pass its "ensuring integrity" bill, with Pauline Hanson and Jacqui Lambie looming as key senators.
Australian Associated Press