The ATO states
Single Touch Payroll for all employers
During November we (the ATO) will write to smaller employers who have 19 or less employees and already use payroll software.
We will tell them about Single Touch Payroll (STP), and remind them they don't need to wait for legislation to pass to start reporting through STP. If their payroll software offers STP they can update and start reporting now.
We will tell them to contact you or their digital service provider if they have questions.
To help you with any queries, see:
ICB Resources for Members to advise their employers with creditable engagement into STP
All Single Touch Payroll Information and Access (Public)
STP Business Information Sheet
STP Information to inform Employees
Introducing STP to your employer (A guide book)
Access to all Single Touch Payroll ICB Resources (Bookkeepers and Business members)