Tax implication on PAYE & UIF for 13th cheque staff payouts

What is the tax implication on 13th cheque pay outs to staff? (PAYE & UIF)

Is it a normal bonus or based on something like a commission earned?

It is a normal bonus (normal salary x 2) eg if I earn R12000.00 per month, the basic will be R24000.00 for the December salary payouts

Then you will be taxed either using the SARS tax rates for R24 000 or if your employer uses the balance of remuneration method they will work out how much tax is due with the bonus and without it and then the tax would be the difference.