Johannesburg - Mineworkers at De Beers will embark on a strike on Friday that will "rock the diamond industry", the National Union of Mineworkers (NUM) said.Peter Bailey, NUM's chief negotiator at De Beers, said the strikers would make their presence felt at the mines."This is the first strike [at De Beers] in many years, but they have pushed us to the point they never thought we would reach."The strike will begin from 6pm this evening (Friday)... We are going to rock the diamond industry with this strike," said Bailey.Spokesperson for De Beers, Wayne Smerdon, said: "That may be their perception, but we do have contingency plans in place... We are always open to negotiation and trying to find ways to resolve issues."He said the company was looking into picketing rules, in light of strike violence in other sectors."It is [NUM's] right to go on strike, but it is also our right to protect our property and those who aren't on strike."That this was the first strike in many years was evidence of De Beers' diplomacy with workers, Smerdon said.NUM served notice of its intention to strike on Wednesday afternoon after talks broke down.The world's largest diamond producer had offered seven percent with an additional cash payment."The very minimum basic salary will be R5 885, which, to put in some context, affects less than 100 employees [out] of 2 818 in De Beers Consolidated Mines," De Beers said on Wednesday.The diamond producer had initially offered a 5% increase. NUM wanted 15%.Another point of conflict was the union's demand for an "agency shop agreement" between De Beers and the union.Under such an agreement, a fee is deducted from non-union members' salaries so that benefits that accrue to them from union negotiations are not free.De Beers was opposed to this because it saw this as a violation of non-affiliated workers' right to freedom of association.De Beers said it was confident it could continue to meet demand from diamond trading company sightholders for supply when the strike got underway. Unlisted De Beers is 45% owned by mining firm Anglo American [JSE:AGL].