Seatbelts in Self-Propelled Mobile Mechanical Plant If its there, then yes it is mandatory.
recently at a H&S forum, it was discussed that a Worksafe inspector was out and about, he was in a business for a totally different issue but saw forklifts and a small excavator in use, upon more inspection it was found that none of the operators were wearing seat belts, the company then got a improvement notice and was advised all workers had to do retraining on all their mobile machinery.