More than three-quarters of Australia's growing army of bicycle fast food couriers are earning less than the minimum wage, the first study of the sector has found.

Most delivery riders on the nation's roads are men, many of whom are from non-English-speaking backgrounds.

The Transport Workers Union (TWU) is today launching a campaign to boost rates of union membership in a bid to improve workplace conditions for the riders.

TWU national secretary Tony Sheldon said thousands of bicycle couriers were being exploited, and many of them were regularly putting their lives at risk without adequate insurance.

"This is wage theft at its worst," Mr Sheldon said.

"A large number of these workers — over 70 per cent — are requiring this work for their substantive means of employment.

"Many of these people are getting injured weekly, but they are receiving no worker's compensation and no sick leave."

The survey of food delivery riders was conducted in Sydney and Melbourne, but Mr Sheldon said its findings were consistent with what union leaders had heard in other capital cities too.

It attracted 160 responses across the two cities, with just under half the respondents saying they had either been injured at work, or knew of others who had.

Colombian Deliveroo rider Anderson does food deliveries in Sydney full time. ( ABC News: Tom Joyner )

One in four said they worked more than 40 hours per week, while about three in four said they worked 20 hours or more.

The TWU claims an equivalent hourly award rate for bicycle couriers would be $24.41, but said its survey found 77 per cent earn less than that amount.

"That's a beginning point that's below subsistence," Mr Sheldon said.

"People are working in some cases more than 80 hours a week trying to etch a living, with the fear that any day they can be bowled over by a car."

Deliveroo pay 'not that great'

Sydney university student Andrew Rickert, 23, used to be a bicycle courier for fast food delivery app Deliveroo.

He said he juggled shifts cycling food around Sydney's Newtown while studying full-time, but ultimately quit the job after pressure from his parents.

"They said, 'Look, you're not earning that much, in the interests of your safety, just stop and we'll cover you until the end of semester'," he said.

Mr Rickert said he received about two hours' training when he started at Deliveroo, but safety on crowded city streets was a constant concern.

Sydney university student Andrew Rickert is a former food delivery rider for Deliveroo. ( ABC News: Laura Brierley Newton )

He said he had heard of other riders being injured on the job, including one who was reportedly knocked over by a cement truck while cycling in central Sydney.

The three main companies in the food delivery sector in Australia are Deliveroo, UberEats and Foodora, which all hire riders under different conditions.

But lawyers say what unites all three companies is that they generally recruit riders as "independent contractors" rather than hiring them as employees.

In Mr Rickert's view, the rate of pay at Deliveroo was previously fairly good, but that riders who signed up after he did were not offered as good a deal.

"People are going to try to work for two of these companies or three of these companies if they can, because sometimes the pay that you get out of it isn't that great," he said.

Gig economy has 19th century precedent

Being an independent contractor rather than an employee means a rider is not entitled to award rates of pay, does not get sick leave and is not covered by Commonwealth unfair dismissal laws.

The Dean of Sydney University's Law School, Professor Joellen Riley, said there was precedent for workers in newer types of labour initially being considered "independent" before being reclassified after unionisation.

"Back in the 1890s, we had an on-demand economy too," Professor Riley said.

"Men would just front up at the docks and wave their hands and hope to get a couple of hours of unloading and loading a ship for a few shillings."

"But it was the pressure of those kinds of circumstances that led to the development of the labour movement and the move towards the notions of a weekly wage and guaranteed work."

In the United Kingdom, the status of delivery riders has recently been reviewed, with a new designation of "worker" recognised to ensure better pay and conditions.

Professor Riley said any change along those lines in Australia would have to be made by Parliament, after a High Court ruling signalled the court was reluctant to shift policy on its own.

"We'd probably first of all need to identify whether the employer is the platform or the app in this circumstance," she said. "That's probably the place you would start."

"If we don't do something to really look at this kind of work … there will be some tragedies if we don't really begin to look this and take care of these people."