Sawmillers and timber traders have criticised the rises, which vary according to log class, and claimed there was little chance of raising sawn timber prices by the same margin.
One trader predicted sawn timber prices to rise by 18%-30% from August.
KLF said its increases were market-driven and have been approved by the South African Forestry Company.
The rises follow the decision of KLF and Bonheur to withdraw from a planned merger. Evidence of price discrimination had arisen during a competition tribunal hearing into the merger.
