Taxis wait for customers outside the Breeze Plaza shoppig malll in Taipei, Taiwan, 20 December 2014. [Photo/IC]

App-based taxi service Uber has been fined for operating illegally in Taiwan.

The highways unit has handed down 30 fines to Uber totaling over $80,000 for operating without a license.

It's a blow to the US company which is embroiled in a number of international disputes.

The authorities have ramped up their investigation into the firm in response to anger from taxi drivers who say their income had been hit unfairly by the app.

Highway authorities have called on people not to use Uber, warning that they may not be fully protected by the law should they encounter disputes or have their personal information leaked.

The company is appealing to the transport ministry over the fines.

Founded in 2009, San Francisco-based Uber is valued at around 40 billion dollars and says it operates in 250 cities in 50 countries and regions.