New figures have shown half of all low-income households own a car, and spend 17p in every pound earned on motoring costs.
The RAC Foundation study "Low Income Motoring in Great Britain" concluded that any attempt by the Government to squeeze more money out of the driving public would have a significant impact, especially on this economic group.
The study shows the lowest earning fifth of all car owning households is the section of society paying more as a proportion of their income on motoring cost.
Trading down during the recession is almost impossible, as people on the lowest incomes already own the cheapest and oldest cars.
According to Professor Stephen Glaister of the RAC Foundation, running a car is "vital" for most people in the UK. He said: "Whilst the wealthier members of society spend more on motoring in absolute terms, it is the poor who pay most as a proportion of their incomes."
He urged ministers not to raise motoring charges, as they will punish the least well off even further.
© Press Association 2009