Residents of an estate which has a new parking contractor were stunned when its wardens "descended like vultures" on the first day and towed 20 cars.
The Victoria Green estate in Edmonton, north London, has just started to use Parking Control Management (PCM) to ensure residents' spaces are protected.
They began on Friday when wardens arrived at 0540 BST and got clamping.
Residents who forgot to display PCM's permit signs got their cars towed - and call it a "cynical money-making ploy".
Cameron Khoshnevif, 31, a sales executive, said: "At about 5.40am I heard chains rattling outside.
"I looked out and saw about four guys already clamping cars.
"It is absolute exploitation - the fact they turned up at 5am shows they just want to make as much money as they can."
About 10 cars were clamped - resulting in a £130 fine - and approximately 20 were towed, incurring a £330 penalty.
Mr Khoshnevif continued: "These companies are employed to protect residents' parking spaces.
"But instead they turn up like vultures to tow away the car of every resident who has made an honest mistake.
"It was a calculated plan to swoop on as many cars as possible."
One driver went into his house to collect money to pay the clamping fee.
He returned within two minutes to find PCM workmen already starting to load his car on to a tow truck.
The driver sat in his car and refused to move until police arrived.
A police spokesman said they resolved the issue peacefully.
Conrad Murray runs a legal advice website. He said: "The residents should take legal action.
"To have people waiting at the gates on the first day to sweep in with clamps is just outrageous."
He continued: "I deal with a lot of parking cases but I have never come across anything like this - it was a military operation."
PCM's motto is: "We are committed to providing a caring, hassle free solution for all of our clients parking needs."
But the AA describe them as a "rogue parking company" and say they will raise the latest incident in a meeting with a Home Office minister next week.
PCM made no comment when contacted by BBC London.