Scores of motorists have been slapped with fines from Smart Parking after the company took over the running of the Bowen Square site and the area behind Waitrose.
Motorists are now restricted to two hours free parking instead of three since the takeover by LCP Properties.
Smart Parking Ltd uses number plate recognition as shoppers enter the car parks. The fine for parking over two hours is £100 (£60 if paid early).
The move has been described as 'commercial sucide' by one Daventry resident.
Therese Collins recently spent £300 in town centre stores in one day.
"I ended up with a £60 fine," she said.
"It's absolutely sickening. It's excessive and disaproportionate to the 'crime'."
Therese has lived in Daventry for four years.
She added: "I've taken Daventry to my heart; I love the town.
"This sickens me. It's commercial suicide."
Dawn Branigan, who owns First Light Photographic & Daventry Framing Centre in High Street, has fears for people's safety.
She said: "At the moment there is just one long stay car park in Daventry in the town centre, which is inevitably full when some of the employees start their shift - one example of this is a lady who works from 2pm until 9pm - given the fact that the car park in town is already full, she has to park in a car park on the outskirts of the town centre and then walk from there - this is fine during daylight hours, but when she has finished her shift at night, she has to walk back to her car in the dark via an underpass with something of a reputation to retrieve her car and go home.
"There are also people living in the flats above Bowen Square - one of them has now had to park her car on her father's drive elsewhere in town, as she no longer has anywhere to park."
People working and living in the town said Daventry has always been known for its free parking.
"To see this eroded by greedy landlords is soul destroying," added Dawn.
"It's out and out greed by the private landlords - it has nothing to do with maintaining the churn of traffic for shoppers - the car park behind me is largely empty now - all day every day."
Daventry mum Kirsty Beeson was landed with a £60 fine for being 16 minutes over the free time limit.
She said: "My ticket didn't even state the time limit. It states my in and out times and then says I didn’t park in accordance with the signage - which said two hours. I literally forgot whilst having a coffee
"What I think is unfair is how the changes will affect disabled people. By not having any concession for blue badge holders it will possibly make life more difficult for those who need that extra time to prepare their day."
The Daventry Express contacted MP Chris Heaton-Harris and the landlords. They had not replied before time of going to press.