Reliance Industries, controlled by Indian billionaire Mukesh Ambani, on Thursday said it had taken the first formal step towards enforcing a claimed right of first refusal on the sale of shares in Indian mobile operator Reliance Communications to South Africa’s MTN.

Reliance Industries said it had written to Reliance Communications, controlled by Mukesh’s younger brother Anil, to begin talks over the claim in a process that could end up in court and which is threatening to scupper one of the biggest emerging markets telecommunications deals in history.