The South African Commercial, Catering and Allied Workers Union (Saccawu) is threatening to halt operations in the wholesale and retail industry in coming weeks.
Saccawu, which has 120000 members across different industries, has marked major retailers Woolworths and Pick n Pay as targets for countrywide strikes for undermining the role of unions within the ranks of employees.
The union declared labour disputes with several other companies, citing "unilateral work-reorganisation, arbitrary change of work conditions and dangerous extended trading hours" as some of the issues under dispute.
Mike Abrahams, Saccawu's media officer, said: "Saccawu is at an advanced stage of membership mobilisation to engage in a series and forms of industrial action ranging from pickets, protests to a full-blown action by members against Woolworths across the industry."
The union said that Woolworths "has used all sorts of feeble excuses to deny union representation of members" as well as the use of 70percent casual workers.
It accused Woolworths and Pick n Pay of a "Walmartisation" of the sector.
American retail giant Walmart, the union said, used anti-union tactics to discourage its employees from joining trade unions.
Bones Skulu, Saccawu general secretary, said: "Central to all these industrial atrocities and unilateral changes are private equity fund activities, raising money from worker pensions to buy out companies.
"Internationally, private equity buyouts have led to the stripping of company assets, leaving them in excessive debt, downward spiral of worker benefits and massive job losses," said Skulu.
Pick n Pay, which is releasing its annual financial results today, would not comment on the allegations made by Saccawu.
Zyda Rylands, chief operations officer of Woolworths retail, said: "Woolworths employee relations strategy remains firmly focused on developing and maintaining sound one-on-one relationships with staff.
"Should a union demonstrate that it is sufficiently representative, Woolworths will grant it the right of stop orders and access," said Rylands.
In 2006 the union organised a strike by Shoprite employees over wage disputes, which lasted nearly three months.