The European Commission has this week launched a public consultation on controversial proposals that could require car manufacturers to make information on fuel consumption and carbon emissions a more prominent component of print adverts and other promotional material.

The proposed rules raise the prospect of cigarette packet-style health warnings on car adverts with manufacturers required to give over a certain proportion of all adverts to information on carbon emissions. The Commission is also reported to be considering a "traffic light" rating system whereby low-carbon vehicles carry green marks while the most polluting cars are designated with red marks.

The proposals, which also include rules that would require carbon emission data to be made available in all car showrooms, are subject to consultation but the Commission has signalled its intention to toughen up the rules governing car advertising.

It said studies have shown that the current CO2 labelling directive "is not working as well as it could and needs to be amended". It added that with cars accounting for 12 per cent of overall EU carbon emissions it is committed to ensuring that consumers have enough information to choose lower-emission vehicles.

The proposals have provoked uproar from manufacturers, advertising agencies and publishers who have all argued that the legislation is unnecessary.

A spokeswoman for the Society of Motor Manufacturers and Traders (SMMT) said that the UK car industry already had to adhere to strict regulation regarding the communication of fuel efficiency in adverts and as such further legislation was not required.

She also argued that the car industry was being unfairly targeted, noting that if CO2 warning labels are to be applied to car ads, there would be a case for similar rules being imposed on other carbon-intensive sectors such as airlines and IT. "You have to ask where it is going to end," she said.

However, environmental campaigners dismissed the industry's objections, claiming that manufacturers frequently fail to comply with the spirit of the existing regulations, often hiding CO2 data in the ad's small print and exploiting a loophole that allows CO2 figures to be omitted from "primarily graphical" information.

Friends of the Earth transport campaigner Tony Bosworth welcomed the European Commission proposals, arguing that it was important for consumers to have " clear and accurate carbon emission data to help them make decisions".

In related news, the SMMT this week provided further evidence that concerns over the environment and rising fuel prices are affecting car sales after data showed that new registrations of 4x4s last month fell 18 per cent compared to May 2007. In contrast, sales of mini-sized city cars climbed 12 per cent, while diesel car registrations rose 8.4 per cent.