The unions, however, say Chinese owners are indeed their biggest headache. And, contradicting the government, the president of the Gemstone and Allied Workers Union of Zambia, Sifuniso Nyumbu, was able to produce contracts with Collum that had the signed and stamped approval of the commissioner’s office as well as letters from the Labor Ministry acknowledging union complaints about the company.

“The Chinese promise to implement a deal, then claim they forgot or there was an oversight,” Mr. Nyumbu said. “The union doesn’t have enough money to keep sending people down to Collum Coal, and when our members there speak up, they get fired.”

The union’s leaders were frustrated by their own feebleness. Early last month, Mr. Nyumbu implored workers to refuse their monthly wages if the payment was docked for work days missed. Solidarity was essential to the protest, and on Oct. 15, when miners at Shaft 2 heard that men at Shaft 3 were accepting reduced pay, they boldly marched up the road, calling for the others to follow the union’s instructions.

They were met at the gate to Shaft 3 by the Chinese supervisors. The Xu family is from Leping in Jiangxi Province, and most of the men they recruit as managers are former miners from the same place, said Xu Jianrui. They live in a modest compound, electric fans chasing the heat from their small rooms. On a recent morning, wet clothes hung on a long wire line outdoors. The carcass of a skinned pig dangled beside them.

The two supervisors who used their shotguns, Xiao Lishan and Wu Jiuhua, refused to be interviewed. But Mr. Xu, who was not present at the confrontation, said one of the men aimed into the air and the other fired into the ground, causing dozens of pellets to ricochet. He said the managers feared for their lives when the mob began heaving stones.

“We had four people injured in the head and thigh,” he said.

A dozen miners, questioned separately, denied anything was thrown. Whatever happened, it was portrayed in much of the local press as an outrage, reminding people of a 2005 tragedy when 46 Zambians died in an accident at a Chinese-owned explosives factory.

Michael Sata, an opposition leader who has long used anti-Chinese sentiment for political combustion, denounced the spilling of “innocent blood” by “merciless so-called investors.” But President Rupiah Banda said singling out the Chinese was unfair. One local newspaper quoted him as saying, “Everyday, people are shot by Zambians, are shot by white people, are shot by the Americans, they are shot by everybody.”