TurtleHunter said..T 11 said..
If you haven't got an ABN your employer must withhold 49% tax of your payment and send it to the ATO
Get an ABN it free
yep profesional advise would be better.
I think your thinking of TFN not ABN T11
This is straight off the ATO website
When a business doesn't quote its ABN
If a business supplies you with goods or services it should quote its ABN. If it does not you must generally withhold 49% from the payment you make to them and send the withheld amount to us.
https://www.ato.gov.au/Business/PAYG-withholding/Payments-you-need-to-withhold-from/When-a-business-doesn-t-quote-its-ABN/