Thousands of workers in South Africa, dissatisfied with low wages and changes to terms and conditions of employment, went on strike on Friday at companies controlled by Walmart-led Massmart Holdings, according to a labor organization.

According to the South African Commercial Catering and Allied Workers Union (SACCAWU), an affiliate of the powerful union COSATU, which is linked with the ruling African National Congress, the indefinite strike will draw more than 18,000 members across the country.

“We expect all members to join the strike,” said SACCAWU spokesperson Sithembele Tshwete, adding that picketing began outside several Massmart stores at 0400 GMT.

The union has said it had exhausted all efforts to resolve labor disputes with Massmart, which owns Game, Makro and Builders Warehouse stores, and was left with no option but to go on strike.

The disputes include a wage dispute at Builders, with unions demanding an increase of 500 rand but Massmart is only offering an increase of 320 rand. The union is also disputing unilateral restructuring and changes to terms and conditions of employment, which includes imposing a 40 hour working week with no premiums.

The union also wants workers who lost jobs as a result of restructuring at general merchandise Game chain to be reinstated. Massmart has said it had identified alternative jobs for those workers.

Tshwete said there were no immediate plans for the union to resume talks with Massmart.

Massmart said the strike could cost striking workers up to 25% of their November wages, if the industrial action was to last for a week.

“It is difficult not to conclude that the… industrial action represents a SACCAWU leadership power play that is not necessarily in the best interests of their members,” Massmart said.

Massmart said contingency plans have been implemented to ensure continued operations, which includes deploying experienced contract employees to its stores.