Tips left by diners at restaurants across Melbourne and Sydney are being taken by owners, often without the knowledge of the waiters the tip was left for, unions and restaurant staff say.

An investigation into the restaurant and cafe industry by Fairfax Media has found brazen underpayment of hospitality workers across the two cities, with little regard for minimum wage rates, workplace conditions such as breaks, or superannuation.

Big tip swindle ... Tips left via credit card payment are a particular problem. Credit:Louise Kennerley

Have you been underpaid working in a Melbourne restaurant? Email Clay Lucas

Over the past two weeks, in reaction to inquiries and reports by The Age and Sydney Morning Herald, scores of hospitality workers have also said they regularly failed to get a share of tips left at restaurants where they worked.