Australian residents for tax purposes can claim the tax-free threshold on the first $18,200 of your income in each income year.

If you have more than one payer at the same time, it’s generally required that you only claim the tax-free threshold from one payer. It’s recommended claiming the tax-free threshold from the payer who pays you the highest salary or wage.

Source: ATO

For more details: https://www.ato.gov.au/Individuals/Working/Working-as-an-employee/Income-from-more-than-one-job/