You must register if you pay Fringe Benefits Tax (FBT). You need to pay Fringe Benefits Tax (FBT) if you provide any benefit to an employee or an employees' associate (e.g. a family member, etc).
Benefits include any rights, privileges or services you supply to an employee as part of their employment, such as covering an employee's gym membership, offering an employee a discounted loan, allowing an employee to use a work car, or providing similar benefits.
FBT is separate from income tax and is based on the taxable value of any benefits you provide. You can process your FBT via your monthly or quarterly Business Activity Statement (BAS).
Please note that volunteers and contractors generally do not attract FBT.