The South African National Union of Mineworkers has given Impala Platinum's Rustenburg mine until Monday to issue a response to its demand for a wage increase.

A deadlock has been reached in negotiations, with the NUM demanding a 16 per cent wage increase and the mine sticking to its offer of seven per cent.

18,000 workers have already marched to the company's offices, but a strike could impact on the entire South African economy. The mine's daily output is in excess of R18 million.

A similar one-day strike in 2002 was estimated to have cost the company R15 million in lost production.

Although protests have been conducted in a restrained manner up to now, some of the activists are threatening an intensification should Implats management ignore their request.

The NUM is also hoping to induce Implats to reinstate some of its members who lost their jobs for participating in last year's strike, which the company declared illegal.

NUM spokesman Aubrey Ntsizi has threatened a full strike if the demands are not responded to.