Sept 5 (Reuters) - South Africa's National Union of Mineworkers (NUM) on Tuesday said it was planning to strike at De Beers' Venetia mine after wage talks broke down, potentially disrupting operations at the diamond giant's new $2.3 billion underground facility.

       NUM, South Africa's biggest mineworker union, said its members were demanding a 9% wage hike, but Anglo American Plc (AAL.L) unit De Beers was offering a 6% increase.

       "The NUM can confirm that the four-month wage negotiations with the world's leading diamond company De Beers have collapsed and a dispute has been declared at the Commission for Conciliation, Mediation and Arbitration (CCMA)," NUM said in a statement.

       The CCMA is a South African statutory body which mediates and certifies outcomes of labour disputes.

       NUM did not say when it intends to begin the strike, but said it was currently working on picketing rules with the CCMA, while mobilising its "more than 1,500 members, preparing them for a protected indefinite strike."

       South Africa's labour laws require workers to give a 48 hour notice before embarking on a strike.

       De Beers was not immediately available to comment.

       In July, De Beers started production from the new $2.3 billion underground mine at Venetia after stopping 30-year open pit mining operations in December 2022.

       De Beers says the Venetia underground mine will produce around 4 million carats of diamonds annually, the equivalent of 12% of its forecast group output for 2023.

       Reporting by Nelson Banya, Editing by Louise Heavens

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