Sibanye-Stillwater and Lonmin said on Wednesday they would seek an urgent hearing from the Competition Appeals Court, after the Association of Mineworkers and Construction Union (AMCU) filed an appeal against a decision by the body approving the merger of the companies.
On November 21, the Competition Tribunal approved the merger with conditions.
The companies said in a joint statement they "remain fully committed to the transaction" which is expected to be concluded in the first quarter of next year. The deal will see Sibanye acquire Lonmin for R5.17 bn, and has received the approval of several regulatory bodies, as well as the South African Reserve Bank.
"Lonmin continues to believe that the transaction represents a comprehensive solution to the challenges facing Lonmin, and offers Lonmin and its stakeholders a more certain future than Lonmin could achieve by any alternative route," read the joint statement.
AMCU Treasurer General Jimmy Gama confirmed the appeal, saying it was based on union's position that the Tribunal failed to take into consideration its submissions on the merger.
"Sibanye are still not willing to protect jobs and have shown that they will go ahead with the retrenchments of workers," said Gama.
The Competition Commission recommended the acquisition on condition that Sibanye takes measures to save about 3 700 jobs.
The companies say the merger would create a "more resilient company, with greater geographical and commodity diversification" – enabling it to withstand short-term commodity price and foreign exchange volatility.
The transaction remains subject to approval by UK authorities.