Former South African President Nelson Mandela's home was bugged during a tumultuous period for his African National Congress party, a prominent labor leader said Thursday.

Zwelinzima Vavi, general secretary of the Congress of South African Trade Unions, said Mandela told him that listening devices were placed in his Johannesburg home, where ANC leaders would come seeking his advice.

Mandela's house was bugged in 2007 during the buildup to an ANC conference at which President Jacob Zuma ousted his predecessor as ANC head, Vavi said. Factions within the ANC were believed to have spied on each other during those tense times....