“I’ll never set foot inside that place again,” said Keith van Eeden, who lives in Strand and was a loyal Spur customer for more than three decades, religiously taking his three children there on their birthdays.

“Spur is only for blacks now,” Mr. van Eeden added. “They don’t want the whites.”

The boycott began in 2017 when Spur sided with a black woman who was in a confrontation with a white man at a franchise in Johannesburg. But the continuing campaign against the chain — promoted by South Africa’s most prominent groups that advocate white-minority rights — reflects something more profound than lingering bitterness over that dispute.

It’s a demonstration of a strong, and what appears to be a growing, sense of resentment among many white South Africans a quarter of a century after they lost political power, and the outrages and brutalities of apartheid were ended.

In the May general elections to elect a new National Assembly, the party that enjoyed the biggest increase in its share of the vote was Freedom Front Plus — a small Afrikaner party fighting to repeal affirmative action policies for black South Africans. The party also opposes the African National Congress’s policy of expropriating white-owned land without compensation, which is not yet law.

In the fight that started the boycott, caught on videos that went viral, the two customers are seen arguing over the behavior of their children. The white man yanks the arm of a black boy, before threatening to hit the black woman and trying to overturn a table where her small children were sitting.