Thousands of club-wielding striking workers at a platinum mine in South Africa were urged by their leaders to remain steadfast in the face of a deadline to return underground Wednesday. The miners gathered at a stadium near the Lonmin operations in Marikana, northwest of Johannesburg, as the world's third biggest platinum producer moved to break a months-long strike. Association of Mineworkers and Construction Union leader Joseph Mathunjwa said his message to the strikers was to "remain steadfast and be peaceful" as armoured police vehicles patrolled the area and a police helicopter circled overhead. Some of the strikers were from an informal settlement near where police shot dead 34 strikers in one day in 2012, after a week of deadly standoffs between rival unions. Lonmin set Wednesday as the deadline to return to work after it bypassed AMCU union bosses to persuade workers to return underground after nearly four months of strikes. A spokeswoman for Lonmin told AFP Wednesday: "Employees are indeed coming back to work but we shall not be providing details of numbers etc -- we should have a clearer idea of critical mass by next week." Mathunjwa condemned "these underhand tactics by Lonmin". "We have lodged a case at the labour court with regard to the employer going directly to our members." He told reporters his message to Lonmin and other platinum producers was: "Don't ever approach the workers individually. "Let's come around the table. Let's get a mechanism of how this demand of the workers can be achieved." - 'Not speaking our language' - More than 80,000 members of the Association of Mineworkers and Construction Union downed tools on January 23 demanding that their basic salary be more than doubled. Mine bosses and AMCU rival the National Union of Mineworkers (NUM) say workers are intimidated into striking, and that many want to return underground. Police were deployed at Lonmin after at least three miners were killed since the weekend, including workers who reportedly defied the strike. Andile Sovendle, AMCU branch manager at Lonmin, denied his union was trying to prevent miners from returning to work. "It's not true. We are not intimidating people," he told AFP. AMCU muscled its way into the platinum belt two years ago with the rallying cry of 12,500 rand ($1,200, 885 euros) in basic salary. "We are on strike until we get 12,500 as basic pay," Sovendle said. "The company is not speaking our language. Our language is 12,500 on basic pay and the company is offering us 12,500 as a total cost to the company which is not what we are on strike for." The world's top three producers Anglo American Platinum, Impala Platinum and Lonmin have offered to up the wage package to that figure by 2017, saying they cannot afford more. But AMCU has rejected the offer and talks have collapsed. The three producers said in a statement Wednesday they would contest a court application by the union to prevent them from extending their offer directly to individual members. "The producers are seeking an end to the strike. To this end the companies have tabled a fair, affordable and sustainable wage offer to AMCU," the statement said. "The companies want to ensure that employees are fully informed of the offer, and that they are empowered to accept or reject the offer of their own free will." Lonmin on Monday said the strike slashed production by 43 percent, reporting a revenue drop of $157 million for six months ended in March. South Africa holds around 80 percent of the world's known platinum reserves.