The appeal related to the oldest case on the authorities' books, which involves allegations of anti-competitive activity by American Natural Soda Ash Corporation (Ansac). Last week the court ruled that "it was not in the interests of justice to hear the matter at this stage".
The constitutional court is the fourth and highest court to reject Ansac's bid to prevent a competitor, Botswana Ash (Botash), from intervening in the case before the competition tribunal.
In August last year the tribunal was the first to reject Ansac's application to have Botash removed.
Ansac made the application after discovering that a lawyer who had worked for the competition commission on the case, and had access to certain information, was now employed by Botash's law firm, Webber Wentzel Bowens (WWB). Ansac also requested that WWB be disqualified from acting for Botash.
When the tribunal rejected this application, Ansac appealed to the competition appeal court, which upheld the tribunal's decision and denied Ansac leave to appeal to the supreme court of appeal (SCA).
Ansac petitioned the SCA. When this was dismissed, it appealed to the constitutional court on the grounds that it had been treated unfairly.
The constitutional court's view that it was not in the interests of justice to hear the matter "at this stage" supports the initial position taken by the tribunal: that until there was evidence that the WWB employee had used his position as a former commission employee to the disadvantage of Ansac, there was no case to argue.
The original case against Ansac relates to a complaint that was lodged with the commission in 1999, shortly after the competition authorities opened their doors.
The complaint, brought by Botash, claimed that Ansac operated as a cartel and thus contravened the Competition Act.
Ansac, the world's largest exporter of soda ash, a key ingredient in making glass, is a group of four large US soda ash companies.
Under US legislation, US companies are allowed to form "associations" for purposes of exporting, but such an association is prohibited from operating on US soil, as it might be deemed to be a cartel, prohibited by US law.