Cosatu has added its voice to calls for a more public investigation of the arms deal.
The union federation commended the ANC initiative to conduct an internal inquiry into the controversial arms deal, but insisted there should also be a more open investigation.
The ANC has set up an internal commission to investigate allegations that some of its leaders received bribes from companies that benefited from the deal.
Opposition parties have demanded that President Thabo Mbeki and the ANC should come clean about their involvement in the deal.
DA leader Hellen Zille has called on Mbeki to establish a judicial inquiry into the deal.
ID leader Patricia de Lille has called on Mbeki and the ANC to say if they received bribes from arms manufacturers. The calls arose from a report in a weekend newspaper alleging that government officials and politicians, including Mbeki, received kickbacks from the arms manufacturers.