The number of complaints about private car clamping firms has soared by more than 50 per cent in the last three years.
Inadequate signage, unfair additional charges and a lack of an appeal process were the main reasons for complaint.
The number of clamping related issues tackled by the Citizens Advice bureau rose from 8,514 to 12,910 between April 2006 to March 2009. Evidence suggested that the penalties were disproportionate to the problems caused by parking, said the organisation.
One example of bad behavior was an elderly lady in Gloucestershire whose car was clamped before she left the car park.
"There is a serious imbalance of power between car owners and private parking companies," said David Harker, the Citizens Advice chief executive.
"The objective of those who demand payment seems to be to make money, not to ensure fair parking. Furthermore, there is currently no right for consumers to appeal fines or seek redress."