Two Hong Kong Uber drivers were fined Friday after pleading guilty to driving without proper licences, the latest slap on the wrist for the global ride-sharing giant.

The pair were among seven Uber drivers arrested in Hong Kong in an undercover police sting in August, as the burgeoning company encounters regulatory roadblocks around the world.

The sting came after furious cabbies in Hong Kong smashed up their own taxis with hammers and drove slowly towards the government headquarters over the summer, calling on the authorities to act over unlicensed drivers.

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San Francisco-based Uber has expanded to hundreds of cities in at least 68 countries, offering new options for both riders and drivers. It is valued at more than $50 billion.

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But traditional taxi drivers remain fiercely opposed, triggering a backlash including violent protests in Brazil where one driver was briefly kidnapped.