The Dalai Lama was to attend a summit of Nobel peace prize winners in Cape Town next month, the first-ever meeting of its kind in Africa.
But, according to an aide, he cancelled after Pretoria denied him a visa in a bid to avoid angering China, which regards the Buddhist monk as a campaigner for Tibetan independence.
"We are deeply concerned about the damage that will be done to South Africa's international image by a refusal -- or failure -- to grant him a visa yet again," the group said in a letter to Zuma.
The Dalai Lama has applied three times in the last five years to visit the Rainbow Nation of Nelson Mandela.
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Each time the government has dragged its heels until the trip was called off.
Each prior rejection has been met with public outcry by South Africans who see it as a betrayal of the commitment to human rights embraced by their government since the end of apartheid 20 years ago.
Two years ago, the country's top court found that the government had acted unlawfully by dragging its heels on a visa application by the Tibetan until it was too late.
"We understand the sensitivities involved -- but would like to point out that His Holiness, the Dalai Lama, no longer holds any political office," the signatories said.
Instead, the insisted, he "would participate in the summit solely in his capacity as a globally respected spiritual leader."
The Nobel summit in Cape Town on October 13-15 is backed by foundations representing four South African peace laureates -- Tutu, Nelson Mandela, FW de Klerk and Albert Luthuli.