JOHANNESBURG (Reuters) - The family of the late Nelson Mandela is furious that a recording of the revered South African leader's voice is being used by the main opposition party for campaigning in local government elections due to be held next month.

In a campaign ad, which the Democratic Alliance (DA) posted on YouTube at the weekend, a young woman steps into a voting booth as Mandela’s voice is heard calling for justice, peace, work and bread. The woman then makes her mark next to the DA logo.

"The DA is doing it to benefit a party which Mandela was not a member of," Mandla Mandela, the grandson of the former president and a member of the ruling African National Congress (ANC) party in parliament, told the ANN7 news network.

The ANC, which Mandela was a long-time member of and once led, has been in power since the end of apartheid in 1994. But it faces a stiff test in local elections on Aug. 3.

The DA hopes to capitalize on a poorly performing economy and allegations of corruption against the ANC.

Responding to criticism from the Mandela family, the DA defended its use of his words. "This great man stood for a nonracial South Africa," said DA spokesperson Refiloe Nt’sekhe.

"The DA is the only party able to take South Africa to the nonracial future it needs. To say that Mandela does not belong to all South Africans is atrocious."

Online media outlet News24 reported that the Mandela family had appealed to the electoral authorities to take action against the DA.

(Reporting by Pete Vernon; Editing by Ed Stoddard and Richard Balmforth)