The MoneySavingExpert (MSE) founder explained how the secondhand marketplace has been told to report earnings their users make to HMRC.
Those who earn on eBay and Etsy or rent their home on Airbnb will also be impacted.
The new rules for these companies make sure anyone who makes more than £1,000 online is declaring their earnings for tax.
On Wednesday evening, Martin tweeted: “Sell on eBay, Etsy or Vinted or rent your home on Airbnb?
“Firms will now report some earnings to HMRC, so check if yours will be and if you need to pay tax.”
Along with his post, Martin shared an article on the MSE website.
It said: “If you sell goods online on sites such as eBay, Etsy or Vinted, rent out your home on Airbnb, or earn extra income from providing services via platforms including Deliveroo or Uber, then these firms will soon start passing on information about you to HMRC.”
A company will only pass data onto HMRC if they’re “selling 30 or more items a year” plus earning more than £1,700 (€2,000).
Under current rules, you can make £1,000 a year alongside your day-to-day job without having to pay tax on it.
If you make more then you have to register as self-employed and pay tax on the earnings.
The MoenySavingExpert website states: “If the total amount you earn via a platform in a tax year is ABOVE £1,000, you LIKELY need to tell HMRC and MAY have to pay tax on this”
Meanwhile, Martin has warned households earning less than £40,000 to do urgent check.
And he reveals how thousands could turn £800 into £5,000.
He recently told how thousands of households can now feel the benefit of switching their energy supplier – and Lewis said it’s “finally” worth a go.
Lewis also went on to explain how shoppers could get £15 a month for free – and it’s so easy to do.
You can also join our new Sun Money Facebook group to share stories and tips and engage with the consumer team and other group members.