As of the 1st of January 2017, taxation rates for working holidaymakers have changed. If you employ working holidaymakers, you must firstly register with the ATO to be able to withhold tax at the working holiday rate.
For employees whose working status you are uncertain of, you can check if they are on a Working Holiday visa (Subclass 417) or Work and Holiday visa (Subclass 462) at http://border.gov.au/vevo using the Visa Entitlement Verification Online service.
The new tax rates only apply to income earned after 1st of January 2017. For earnings up to $37,000 taxation is a flat rate of 15% – for income higher than this, you must apply for foreign resident tax rates.