(IDEX Online) - Petra could axe 150 miners' jobs at its Koffiefontein mine, in South Africa, say union leaders.The National Union of Mineworkers (NUM) says it is "deeply angered" by the move.Mosepedi Sanane, regional secretary for the Kimberley area, said: "We believe there are other avenues that could have been looked at before going through this process which are going to see our members and employees at large losing their employment for good."He said the union had received official notification of "restructuring/ retrenchments" which could impact 150 jobs.Petra, a UK-listed miner, last month announced over $140m of sales at its latest rough tender, and said prices had surged on strong demand.It operates three underground mines in South Africa - Finsch, Cullinan and Koffiefontein (pictured) - as well as the open pit Williamson mine in Tanzania.Petra said in a statement that it had " sought various means to curtail negative cash flow" as part of a business re-engineering project initiated at Koffiefontein in July 2021.