Coles and Woolworths workers will stop manning checkouts and stocking aisles across the country to protest "poverty" wages, unsafe workplaces and job insecurity.
About a thousand workers will strike for two hours from 10am on Saturday in the first national supermarket strike in Australian history, the Retail and Fast Food Workers' Union (RAFFWU) says.
But Coles and Woolworths say customers will notice little difference, with the vast majority of their workers represented by the Shop, Distributive and Allied Employees' Association (SDA), which will not be taking part.
RAFFWU members account for fewer than 500 of Woolworths' 132,000 supermarket employees and less than 0.4 per cent of Coles' workers.
Nevertheless, the strike will be significant for the workers involved, who are beginning to find their voice in an industry that has historically treated them with contempt, RAFFWU secretary Josh Cullinan says.
"These workers are treated like garbage," he told AAP.
"They pay them poverty wages, they don't treat them with any level of respect when crimes are committed in stores and they don't have job security.
"They're fed up with being threatened by someone and worrying that when they finish their shift they'll see them in the car park with a shiv."
While the impact on the supermarkets would be minimal, Mr Cullinan said workers were learning about their power and would be prepared to take more significant industrial action during the Christmas busy period.
Employees will also take limited industrial action on Friday, refusing to perform some tasks including cleaning up vomit or bodily fluids and cleaning the manager's toilet.
While Woolworths will pay workers who engage in limited work bans, Coles says it will not pay workers who refuse to carry out tasks, claiming they are essential components of their roles.
RAFFWU has set up a fund to support Coles workers who lose pay for engaging in the limited strike action.
Despite the strikes, Coles maintains the parties are collaboratively engaged in working out a new enterprise agreement.
"Coles is committed to delivering an outcome that balances the needs of our team members, the sustainability of our business and ensures we can continue to deliver great value and experiences for our customers," a Coles spokesperson said
Both Coles and Woolworths recently passed on the Fair Work Commission 5.75 per cent minimum wage increase to employees.
"We have a long history of bargaining in good faith with our team and will continue to do so," a Woolworths spokesperson said.
"However, we acknowledge and respect the right of team members to take protected industrial action."
The SDA is in the early stages of negotiations with the supermarkets and says it is focusing on securing better wages, fairer and more predictable rostering and five weeks' annual leave.
"Their recent profit announcements demonstrate that they are in a financial position to address the union's claims seriously at a time when its employees are facing significant cost of living pressures," SDA national secretary Gerard Dwyer said.
