By Ed Stoddard JOHANNESBURG (Reuters) - South African platinum producer Lonmin is preparing to restart operations next week after taking its latest wage offer directly to striking miners, hoping to end the country's longest and most costly strike. The 15-week strike over pay by the Association of Mineworkers and Construction Union (AMCU) has also hit Anglo American Platinum and Impala Platinum, jointly costing them about $1.5 bln in revenue. "Our shop stewards are saying that Lonmin management has been going around this week to all the shafts to prepare for the start up on the 14th," an official with a rival union to AMCU told Reuters. Wage talks collapsed two weeks ago and the three producers of the precious metal have been trying to undermine AMCU's leadership with direct appeals to the strikers, betting that they are keen to return after going so long without pay. AMCU's main union rival the National Union of Mineworkers (NUM) said on Friday that many of its workers, who had not been on strike and had been prevented from returning to Amplats' shafts, were now showing up. Lonmin has been asking its employees through text messages and other means to indicate if they want to accept the latest offer and return to work and the company has said it should know by Friday if it can go ahead with the May 14th start. In an internal memo sent to its employees last week and seen by Reuters, the company spelled out the steps to be taken and said employees had until Thursday, May 8 at 1600 local time (1400 GMT) to send their replies. It also provided a toll-free Help Line number for workers with questions about the offer. SECURITY "If we have sufficient take-up, a reminder SMS will be sent and logistics will be arranged in terms of transport and security provisions around return to work," the memo said. "The safety and security of our employees remains our number one priority and additional security will be in place during and immediately after this start-up period." Security will be regarded as crucial as the companies say AMCU is using violence and intimidation to keep its members in line, allegations the union has denied. NUM General Secretary Frans Baleni told Reuters that over the past three weeks the number of its members returning to Amplats' Rustenburg mines was up about 40 percent and 3,000 to 4,000 of its members were back at work. He also said some AMCU members including defectors returning to NUM were among them. NUM was dethroned from the platinum belt in 2012 when AMCU poached tens of thousands of its members in a brutal turf war that killed dozens of people and triggered a wave of wildcat strikes that year. "All of the Anglo mines around Rustenburg have been a hot spot of intimidation. But our guys are now moving from their homes that they were renting and are moving around to avoid being targeted," Baleni said. James Wyatt-Tilby, a spokesman in London for Anglo American, Amplats' parent company, said workers had been trickling back to its shafts. "We are seeing a steady increase of employees from all unions returning to work across the strike affected mines and we call on all employees to follow suit," he told Reuters. "We know from a large number of employees that while they want to return to work, many are fearful of doing so due to unacceptable threats to their personal safety." A critical mass of workers would be required to get its strike-hit and labour-intensive operations going again. AMCU officials were not immediately available for comment. Implats said on Thursday it was also conducting an SMS vote on the offer late this week. The companies are offering increases of up to 10 percent that they say would raise the overall minimum pay package to 12,500 rand ($1,200) a month by July 2017, including cash allowances such as for housing. AMCU had initially demanded an immediate increase to 12,500 rand in the basic wage, excluding allowances, but softened that stance in March to staggered increases that would amount to 12,500 rand within three or four years - still a third more than what the companies are offering in basic salaries. The companies say they were bleeding cash even before the strike. Underscoring the industry's woes is the muted reaction of the platinum price to the strike. Spot platinum is fetching around $1,425 an ounce, a bit lower than its levels on the eve of the stoppage.