Unions have hit back at claims the government's contentious industrial relations reforms would unfairly affect small businesses.
In a bid to secure crossbench support to get the workplace bill through the Senate, Labor is likely to change the size of small businesses that would be exempt from bargaining from 15 to 20 workers.
ACTU president Michele O'Neil said employees at any size business had the right to bargain.
"This is big business running a scare campaign about what is going to happen to small business," she told reporters in Canberra on Thursday.
"(Small business workers) are already excluded in what the government has put through for businesses less than 15 (workers) and they have absolutely nothing to fear from us."
The bill faces an uncertain future in parliament, with the government still negotiating with key crossbenchers including independent senator David Pocock.
Senator Pocock, who will reportedly meet with Mr Burke on Thursday, has said he supports 85 to 90 per cent of the bill but wants time to consider the impact of more complex aspects such as multi-employer bargaining.
Ms O'Neil said the ACTU was also in talks with Senator Pocock.
"We will talk to whoever we need to talk to, to make this bill a reality because it's urgent," she said.
"The longer we take to make a better and fairer system, the longer it will take before we see wages starting to increase."
The comments followed a new report by the unions saying multi-employer bargaining would narrow the gender pay gap.
The 12-page ACTU report says women on collective agreements earn $102.60 more per week on average than women not covered by collective agreements.
"Gender equity is a matter that can be bargained for and included in collective agreements," it adds.
The research notes progress in narrowing the gender pay gap has flatlined and even regressed in some sectors.
The gender pay gap is 14.1 per cent of full-time ordinary time earnings between women and men, or about $263.90 per week.
Independent MP Zali Steggall said she expected there would be further changes to the workplace laws, including increases to the definition of small businesses.
"My discussions with the government have been a bit frustrating because they keep saying 'it's not the vibe of the thing, we don't intend for it to capture these businesses' but the reality is the legislation does capture those businesses," she told Sky News on Thursday.
"I want to see protections so that small businesses are safe from (being caught up in multi-employer bargaining) because I don't think anyone will win."
Shadow treasurer Angus Taylor said Australia didn't need a return to a "toxic" industrial relations system, stating individual arrangements were working best.
"The last (wage price index) data that came out ... we saw individual arrangements going up twice, or even four times faster than union-driven arrangements," he told ABC Radio.
"It's allowing employers and employees to sit down and work together to get the best possible outcome for the business and the workers."
© AAP 2022