If you have more than one payer at the same time, the ATO generally require that you only claim the tax-free threshold from the payer who usually pays the highest salary or wage (this is known as the primary source of income).
If you earn additional income (for example, from a second job or a taxable pension), your second payer is required to withhold tax at the higher ‘no tax-free threshold’ rate. If your second payer does not withhold a higher rate of tax, this may lead to a tax debt at the end of the financial year.
However, if you are certain your total income for the year will be less than $18,200 you can claim the tax-free threshold from each payer.