The labour action came without notice and was related to wage demands, Bombela said in a statement.
The Gautrain bus operating company, Mega Express, was talking with the drivers in an effort to resolve the situation.
Bombela said service updates would appear in the media and at www.gautrain.mobi and www.gautrain.co.za.
Passengers could also call 0800 Gautrain or 0800-428-87246 for more information.
The Gautrain train services were operating as normal, Bombela said.