One-third of drivers involved with ride-sharing services such as Uber are yet to register for GST or to fully declare their income.

Assistant Commissioner Tom Wheeler said more than 100,000 individuals have received a payment for a ride-sharing service since the Australian Taxation Office started collecting data in August 2015, but about one third of them still have not registered for GST and/or fully declared income.

The ATO has written to 60,000 drivers looking to make extra cash by transporting passengers on popular ride-sharing services, reminding them of their obligations.

Uber and other ride-sharing drivers must be registered for GST following an ATO ruling that took effect in August 2015. Before that they had been able to avoid GST payments by arguing they fall under the $75,000 turnover threshold at which GST applies.