Platinum producers Lonmin, Impala Platinum, and Anglo American Platinum will oppose a court application by Amcu over its direct communication with striking employees.
In a joint statement on Wednesday, the three companies said its efforts to end an almost four-month-long strike was not in contravention of regulations or agreements.
"The producers reject claims made by Amcu that any of [its actions] contravene the Labour Relations Act, recognition agreements or employees' constitutional rights," it said.
The companies would ask the court to endorse their communication efforts to find a resolution.
Sake-Beeld reported that the Association of Mineworkers and Construction Union had applied for an urgent court interdict to stop the mines from communicating a new wage offer directly to workers.
The application was filed in the Labour Court in Johannesburg on Monday.
Amcu wants the court to stop the companies from directly contacting some 70,000 workers.
The mines have been communicating directly with their employees for the past two weeks to convince them to accept a new wage offer made in April.
This came after the employers' talks with Amcu leaders deadlocked.
Amcu argued in court papers that the SMS campaign and pre-recorded phone messages to workers from the companies breached the recognition agreement with the mining union. The court will hear the application on Tuesday, according to the newspaper.
Amcu members at the three companies in Rustenburg and at Northam in Limpopo downed tools on January 23 demanding a basic monthly salary of R12,500. The strike has cost the companies about R14 billion in revenue and workers have lost over R6bn in earnings.
Lonmin warned that it might implement restructuring that could lead to job losses if striking employees failed to return to work on Wednesday.
The companies offered Amcu a settlement on April 17. They tabled a wage increase offer of between 7.5 percent and 10 percent.
The proposed offer would have seen the minimum cash remuneration for entry-level underground workers rise to R12,500 a month, or R150,000 a year, by July 2017.