The Association of Mineworkers and Construction Union, majority worker group at both mines, will give the 48-hour notice on Monday, its president Joseph Mathunjwa confirmed to AFP in a text message.
Workers at the firms, world number two and three respectively, voted in favour of downing tools as they demand a minimum salary of 12,500 rand (USD 1,440).
The union will have talks with members at world number one producer Anglo American Platinum later this week.
AMCU claims the current entry-level wage is around 5,000 rand, though gold and platinum producers give higher figures.
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The 100,000-member union also said this week it will strike at gold mines where it is the minority labour grouping.
It has rejected eight-percent wage increases offered by platinum and gold producers.
Following official processes for strikes marks a change from AMCU's past practice of wildcat stoppages since it gained prominence on the platinum belt two years ago.
It wrested control of platinum mines from the government-linked National Union of Mineworkers then with promises of dramatic salary increases.