This according to the official Twitter account for The Gautrain.
At 6.30 am on 12 January they tweeted that bus drivers had not reported for duty that day and that the bus service would therefore be suspended.
Yet the Gautrain train schedule continues to operate.
Our bus service won't be operating as of this morning. Drivers haven't reported for duty. We apologise for the inconvenience.
— Gautrain (@TheGautrain) January 12, 2016
It is unclear yet whether the failure of drivers to report for duty is part of a strike.