The NSW government has begun cracking down on the "ride-sharing" component of the smartphone app Uber by issuing $2500 fines and threatening legal action against motorists who offer the service.

The Uber app allows any motorist – not necessarily a licensed taxi or hire-car driver – to receive money for providing lifts, in addition to offering authorised taxi and private hire-car services.

Under fire: An Uber driver demonstrates the ride-sharing service in Tokyo, Japan. Credit:Bloomberg

The crackdown by NSW's Roads and Maritime Services follows similar action by the Victorian government in early May. It issued more than $50,000 worth of $1700 fines to drivers.

In one letter sent to an unidentified Sydney Uber driver and posted on the broadband forum Whirlpool, Roads and Maritime Services says it is in receipt of information that the driver "may be operating a public passenger service without the appropriate authorisation, accreditation and license". Roads and Maritime Services confirmed to Fairfax Media that the letter was genuine.