"The [Corruption Watch] board members emphatically affirm that no unions are presently being investigated," Corruption Watch said on Tuesday.
The Mail & Guardian reported on Friday that Corruption Watch was investigating leaders of at least four Cosatu affiliates for alleged corruption related to their union members' investment money.
The M&G reported that two Cosatu sources alleged that the union leaders being investigated included the general secretary of the South African Transport and Allied Workers Union, Zenzo Mahlangu; the general secretary of the Chemical Energy Paper Printing Wood and Allied Workers Union, Simon Mofokeng; and several leaders of the Police and Prisons Civil Rights Union.
Corruption Watch says it received 1 500 cases of corruption from the public in 2012, of which only 13 of those implicated unions.
A preliminary investigation was conducted on one union case and the matter was dropped when it was established that the case did not meet Corruption Watch's investigations criteria.
"The board can unequivocally state that no member was aware that there had been 13 complaints brought against any union prior to the M&G report … nor has any member of the board been instrumental in bringing such a report to the attention of the Corruption Watch," it said.