Australians who have taken up a side hustle in the last 12 months are being warned they could soon have a tax bill on their hands. The latest data shows nearly one million people have more than one job, and the Australian Taxation Office (ATO) has already said it will pay very close attention to them.

If you've been doing some Uber Eats delivery, OnlyFans content, or e-commerce selling on the side, you could get a 'shock' after July 1. CPA Australia tax lead Jenny Wong said this could be huge for some people.

“Until this year, individuals have been required to self-declare the income from their side hustles," she said. "Now nothing will go under the radar."

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The Sharing Economy Reporting Regime has been expanded, and it means any company you make money from, be it Airtasker, Doordash, or YouTube, will report that income to the ATO.

The tax office will have a much wider understanding of your income than ever before.

"These rules apply to a broad range of services, not just the most well-known," Wong said.

"If you use a website to rent out a car parking space or your designer handbag, this income will be recorded, and you’ll need to pay tax.”

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Who could get the biggest tax bills?

Wong predicted influencers and X-rated content creators could be in for the biggest tax bills because of the enormous amount of money they can make.

These creators have been reminded that they have to declare any gifts or gratuities they received been July 1 to June 30 as a form of payment.

You have to start paying tax for anything earned over $18,200.

"If you’ve had a successful year earning money through advertising revenue and streaming subscriptions, as well as through gifts and gratuities, the ATO will be expecting you to cough up," Wong said.

"Yes, this even includes free cars, holidays, clothes and anything else you’re lucky enough to receive as a form of payment.

“Depending on how much you’ve earned during the year, this could be a significant amount, maybe even tens of thousands of dollars.”

'It's not just a hobby': ATO going after side hustles

Yahoo Finance contributor and director of tax communications at H&R Block, Mark Chapman, said many people haven't been properly declaring their extra cash from their side hustles.

"You might think your side hustle is just a hobby but the ATO will disagree," he said.