On Tuesday, the council will vote on a plan to make car-share companies pay more for their spots on Melbourne City Council's streets. Companies would also be forced to find two off-street parking spots for every new on-street space.

At present, operators pay $3000 for each of the 21 on-street parking spot on the CBD's "Hoddle grid", and get spaces for free elsewhere.

The council aims to get 2000 shared cars within Melbourne – with the council providing 600 on-street spaces and car-share companies the remaining 1400 in privately owned, off-street spaces.

But the companies and a sole councillor opposing the move say the plan could kill off car sharing.

"This will jeopardise the viability of a fledgling sustainability industry," said Stephen Mayne, the only city councillor against the plan.

His alternative proposal would not make car-share firms provide extra off-street parking. And he wants more detail on 270 on-street parking spaces the council provides to taxis for free.

A council report found that each car-share spot equates to 10 less cars owned by residents or businesses and that there were now 2000 fewer cars in central Melbourne than if car-share schemes did not exist.

But Melbourne's six per cent of residents who are car-share scheme members pales in comparison to Sydney's 20 per cent.

Melbourne has 245 shared cars on its streets compared to 800 in Sydney.

The report found car sharing provided a net benefit to the city of $9 million each year – and a benefit cost ratio of more than $3 for every $1 invested.

The plan going to Tuesday's council meeting "outsourced" to car-share companies the problem of finding more parking for their vehicles without any real idea of the impacts, Cr Mayne said.

But the Lord Mayor said the three car-share companies with parking spots on CBD streets – GoGet, GreenShareCar and Flexicar – were private firms gaining a significant public subsidy.

The companies were desperate to protect these subsidies, Cr Doyle said. "[Flexicar's parent company Hertz] has a market capitalisation of nearly $3 billion," Cr Doyle said.

He said it was "galling to be accused of not supporting car share" because the council wanted to expand it, and had been "very accommodating" finding on-street spaces for existing vehicles. "This is a pro car-share policy," he said.

And Cr Doyle bristled at the comparison to Sydney, which does not provide any CBD spaces for free to car-share operators.

The car share industry is dependent on councils for support, and several councillors who were granted access to some companies' financial reports said it was clear some were barely breaking even.

Both GreenCarShare and Flexicar have told councillors they will pull out if the plan proceeds.

GoGet general manager Justin Passaportis​ said the extra costs would be passed on to members, and that the plan would harm the council's green business credentials. "Why should local residents who give up their car and do the right thing by the environment be penalised by this council?"

Another car-share chief executive, Sahil Bhasin​ from GreenShareCar, said the council was simply trying to maximise parking revenue. "These guys don't care about the environment – they want the cash from parking."

One car-share member, Mike Flattley​, uses the service at home and at work. The executive director of the Royal Society of Victoria, Mr Flattley doesn't own a car, and Royal Society staff also use car-share vehicles as a sort of corporate fleet.

He said Melbourne City Council's plan was wrong-footed.

"If this was a private corporation making immense profits and the council was missing out, there would be a case for it," he said, "But it's another decade before they are really viable, sustainable profit-making businesses."

FACT BOX

•  What is car sharing?

Pioneered in Switzerland and Germany in the late 1980s, car sharing has spread internationally, coming to Melbourne around 2004. Members who join a car-share scheme can access a car on the street or in a public or private car park. They typically pay around $10 an hour, or $80-100 a day, to use a car, with all petrol costs included.

• How many cars are there?

There are 245 in Melbourne City Council's areas, and around 600 more across the rest of Melbourne.

•  Why do car-share companies want on-street spots?

To raise awareness and attract members – there is a clear preference from members for on-street spaces.

•  Why does the council want them to pay more?

The council argues it is providing private companies a public subsidy worth upwards of $600,000 each year. There is also a finite amount of street space, and fierce competition for parking spots and other uses for the space.

•  What do operators pay now for CBD car share spaces?

Operators pay $3000 for each of the 21 on-street parking spot on the CBD's "Hoddle grid", and get spaces for free elsewhere.

• What will they pay under the new plan?

The same $3000 for existing Hoddle grid spaces and $1500 for a new space in the first year, rising to $3000 in successive years. Outside it, spaces will cost from $100 up to $2000 a year.