Tens of thousands of workers at the world's three top platinum producers were set to down tools Thursday in a pay strike that could have a devastating impact in Africa's largest economy. Up to 80,000 workers at Impala Platinum, Anglo American Platinum and Lonmin mines will embark on an indefinite strike from early Thursday, after their demand to double the minimum monthly wage to $1,150 was rejected. Mine owners fear the strike could spark violence in the restive platinum belt where over 40 people, were killed during a wildcat strike in 2012. But police have promised to step up security. As a precautionary measure, the leading platinum producers said they would begin shuttering operations Wednesday night. The wage dispute has pitted the hard-line Association of Mineworkers and Construction Union (AMCU) against mining firms, in a conflict neither can afford to lose. After promises of vast wage hikes lured hard-up workers from rival unions, AMCU must prove to members it can deliver. The strike is aimed at "forcing the employers to the negotiating table", said AMCU secretary general Jeff Mpahlele. Platinum firms, reeling from previous industrial action and facing growing competition abroad, must prove to boards and shareholders they still have a viable business model. There was a partial reprieve for the gold sector, however, with AMCU delaying strike action -- also slated for Thursday -- until a labour court rules on the legality of a work stoppage. But in the platinum sector, mines already began shutting down operations late Wednesday, amid fears of a rerun of labour violence that has killed dozens. "We have commenced safe shutdown procedures at operations where AMCU is the majority," Anglo-American Platinum (Amplats) spokeswoman Mpumi Sithole told AFP. Impala Platinum (Implats) said they had also taken a decision to freeze operations. The company will close all its mines and smelters "to ensure we mitigate the risk of intimidation and violence as far as possible," Implats spokesman Johan Theron told AFP. "The safety and security of our employees is our number one concern." In previous strikes non-union staff and members of rival unions have reported being threatened if they refuse to take part. And in August 2012, some 34 striking miners at Lonmin were shot dead by police amid violence that killed around a dozen more. Police spokesman of the North West province Thulani Ngubane told AFP "police are ready to protect Marikana" and will deploy enough forces for the numbers expected to go on strike. Ian Cruickshanks chief economist with the South African Institute of Race Relations sees it unlikely that the strike could turn as violent as the 2012 Marikana protests because of the preparations that have gone into the latest wave of strikes. "I think it is a fairly low level risk," he said. Theron said Implats' planned lock-out is a legal process and would last "for as long as is required," but operations could resume if enough staff ignore the strike. Lonmin said no firm decision had yet been taken on whether to shut down operations. "We obviously expect a strike from the morning shift tomorrow and we'll make some decisions when that occurs," said Lonmin spokeswoman Sue Vey. As many as 80,000 workers are expected to stay away from the mines, causing ripples across the South African economy and the world. Labour Minister Mildred Oliphant is trying to organise talks with the union on Friday. "Our economy is stressed enough already and another strike in the mining industry would have dire consequences," said the minister. South Africa is the world's largest platinum producer and around 134,000 workers employed in the sector. Platinum and related metals are used in products from catalytic converters to computer hard disks to dental fillings. Amplats, Implats and Lonmin issued a rare joint statement on Tuesday, describing union wage demands as "unaffordable and unrealistic" and warning previous industrial action had already cost jobs. The trio warned that previous strikes, rising operating costs and a sharp drop in platinum prices had resulted in the loss of around 11,000 jobs since December 2011. They also claimed strike action directly cost them $1.2 billion in lost revenue and workers lost $110 million in lost wages over roughly the same period. But unions are adamant that the country's mining firms, with billions of dollars in revenue, can afford to pay out more. Anger at vast income disparities is raw in a country that even 20 years after the end of apartheid remains one of the most unequal on earth.