But fundamental points of difference between unions and big business remain, including what changes should be made to the bargaining system.

Changes to fix to workplace bargaining and a boost to the annual migrant intake have emerged as the major topics of debate ahead of the summit.

Prime Minister Anthony Albanese is hoping the Parliament House summit heralds a new era of cooperation between business, unions and governments, which he argues is critical to addressing problems including falling real wages, skills shortages and the gender pay gap.

There is evidence that is already happening as the countdown continues to the start of the summit on Thursday.

The Australian Council of Trade Unions and the Council of Small Business Organisations Australia announced an agreement to cooperate on simplifying and reducing complexities within the current industrial relations system.

That includes a pledge to support new options for collective bargaining, flagged last week by the ACTU, which would enable multiple workplaces to band together to strike deals with employees.

"Small business have been looking for a way forward that suit their unique needs for a long time," the small business lobby group's chief executive, Alexi Boyd, said.

"We do not have resources that are available to big business with lawyers and HR departments. The current bargaining system was not built for us, it is not efficient and is too complicated."

Although the finer details of the agreement have yet to be thrashed out, Ms Boyd stressed that small businesses wouldn't be forced to sign up.

Employment Minister Tony Burke told ABC's RN Breakfast that the deal was "exactly the sort of cooperation we've been hoping to achieve with the summit".

But opposition employment spokeswoman Michaelia Cash said small business should be "very cautious about inviting unions in their workplace".

"By the admission of [Ms] Boyd, the devil will be in the detail and that detail has not been worked out yet," she told The Canberra Times.

"We will await that detail and monitor the process as it unfolds."

While the small business group is open-minded to so-called multi-employer bargaining, the Business Council of Australia - which represents many of the nation's largest companies - remains concerned it could lead to unintended consequences.

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But Business Council of Australia chief executive Jennifer Westacott said there were areas of agreement with unions, including a shared belief that the bargaining system needed to be simplified in order to deliver higher wages for workers.

Ms Westacott said the summit should be about finding common ground, not creating a competition between workers and employers.

"Of course, there'll be differences. We don't agree with the multi-employer bargaining in the way it's been described," she told reporters at Parliament House.

"But it's absolutely important that we remember this. We cannot get industrial relations reform in this country to stick if business and unions don't come together and find some middle ground."

National employer association Ai Group claims existing issues within the enterprise bargaining system does not justify radical reforms outlined by the ACTU.

"There is a lack of detail about how precisely the unions' multi-employer, industry-wide bargaining proposal would work. However, there is reason for extreme caution when considering it," Ai Group chief executive Innes Willox said.

"The key problem is that the bargaining system is now too complicated and operates in an impractical manner. Agreement making should be a simple process for employers and employees - not the 'minefield' that it currently is."