The Association of Mineworkers and Construction Union refused to sign a "peace accord" with British mine owner Lonmin PLC, the world's third-largest platinum producer.
Its representatives said they were not interested in a deal that failed to include a wage increase to about $1,500 a month, nearly triple what workers make now.
Representatives for the wildcat strikers at the Marikana mine near Rustenburg, about 80 miles northwest of Johannesburg, also refused to sign the deal.
Several other unions, including the country's largest trade union federation, did sign it.
The accord calls for an end to violence and for striking workers to return to the mine by Monday.
Lonmin said in the deal that after platinum production resumes, the company would discuss workers' demands for salary increases. The AMCU said it wanted the wage-increase demands fulfilled before returning to work.
The Marikana strike began Aug. 10, when 3,000 rock drillers stopped working and demanded the higher wages.
Early clashes among workers left 10 people dead. A mass protest Aug. 16 ended with 34 additional strikers dead when police fired live ammunition into a crowd of men armed with clubs and machetes.
Lonmin said Thursday it remained "hopeful" the AMCU and representatives of the wildcat strikers would sign the accord and join the wage talks, which would amend a two-year agreement that ends next year.
"Lonmin and the other unions who are part of our bargaining council have agreed to negotiate to address the wage demands within a legal framework and have invited AMCU and a delegation of workers' representatives to take part," Lonmin acting Chief Executive Officer Simon Scott said in a statement.
"We simply ask that those negotiations happen in an environment free of intimidation and violence," he said.
Less than 2 percent of workers reported to the Marikana mine Thursday amid reports of widespread intimidation, The Wall Street Journal said.
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