The National Union of Mineworkers (NUM) marched in Secunda on Saturday to demand recognition at Sasol Mining as the apparent majority union.
"At Sasol Mining we started organising last year and we now have a majority," said NUM spokesperson Lesiba Seshoka.
"We have about 1 300 members out of the 2 200 workforce at Sasol Mining."
The Chemical Energy Paper Printing Wood and Allied Workers Union (Ceppawu) is the other union represented at the mining company.
Seshoka said Sasol Mining management were handed a memorandum on Saturday giving them seven days to recognise the union.
Seshoka said the union was "confident" their demands would be met.
"Strike action is always the last resort."
Sasol spokesperson Jacqui O'Sullivan said a dispute has been declared at the Commission for Conciliation, Mediation and Arbitration (CCMA).
She said that a meeting with the CCMA would take place later this month which would independently verify whether NUM had met the required threshold for membership.
Seshoka said a date had not yet been set for this meeting.
O'Sullivan said Sasol would follow "due process" to resolve the matter.
"Sasol is committed to working with unions, where the required threshold representation has been achieved, a recognition agreement is in place and the necessary partnership charter has been confirmed," she said.—Sapa.