Union Saccawu is the fifth Cosatu affiliate to write a letter to the federation president Sdumo Dlamini, calling on him to convene a special congress.
Saccawu members of the National Bargaining Council for the Road Freight and Logistics Industry will strike for wage increases, the union has said.
Unions, the ANCYL and YCL have vowed to disrupt a DA-led march on Cosatu's headquarters, warning it will mark the beginning of "open class warfare".
Saccawu says Walmart could pursue its "anti-union philosophy" if its merger with local retailer Massmart goes ahead in its current form.
Cosatu and Saccawu have announced their intention to embark on "mass pickets" at the Walmart-Massmart appeal hearing in Cape Town this week.
Saccawu wants Walmart and Massmart to increase their planned fund to support SA suppliers from R100-million to at least R500-million.
Cosatu has expressed "shock" at Pick n Pay's announcement that it is contemplating retrenching about 3 137 workers.
The Competition Tribunal has Âcriticised the government's call for procurement quotas to apply to the Walmart-Massmart merger.
Massmart's chief executive said that the group's management team welcomed the prospect of becoming part of the Walmart family.
The state's opposition to the Walmart/Massmart merger is sending the wrong message to corporate South Africa, argue stakeholders.
A US labour expert testified at the Competition Tribunal hearing in Pretoria on Thursday Walmart's bid to acquire a controlling stake in Massmart.
The Walmart/Massmart merger hearing continued on Monday as a former Walmart executive was grilled on the company's perceived hostility towards unions.
The Competition Tribunal has given unions an additional 15 days to present more evidence against Wal-Mart's $2,3-billion bid for Massmart,
If Wal-Mart succeeded in its bid to buy a share of Massmart, it would mean job losses for the retail and manufacturing sector, union Saccawu said.
About 27Â 000 Pick n Pay employees are preparing to go on a protracted strike after the company failed to meet their demands.