A fault across three separate ticket machines at a private Northampton town centre car park meant fines were issued to motorists who paid to park for the whole day.
Customers who bought the 'early bird special' at the NCP car park off St Peter's Way and were still issued a penalty in the past month are being urged to check again and think about appealing the fine.
NCP was made aware of the fault after several workers from the same office in Northampton - who park all-day on a regular basis - told the Chronicle and Echo they were all fine on certain days across the space of a month.
One worker from the County Couty Business Centre, Ingrid Khan, said: "I regularly pay for the early-bird ticket to stay all day, so it's not I fell I would get wrong. But then my other colleagues were fined too.
"It's not like we keep out tickets for a whole month to prove it. What are we meant to do?"
In fact, six colleagues from the County Court Business Centre in Katherine Street told the Chron they were hit with £60 penalties across the space of a month after paying early in the morning to park in town all day.
Two people claimed they had been fined for staying on October 10, and three people were penalised for their stay on September 30.
As a result, NCP found that on October 10, all three ticket machines in St Peter's Way had malfunctioned for a short period and resulted in customers being fined.
They also found a machine was faulty between September 28 and October 2 - but also claim this one would have displayed it was 'out of order' if anyone tried to use it.
It means anyone who feels they have been unjustly fined and have thrown away their tickets as proof of purchase will need to show a bank statement as evidence they bought they paid to stay if they hope to have their penalties appealed.
This, however, leaves anyone who pays with change without an option.
A spokeswoman for NCP said: "We were aware of a technical fault that occurred on all 3 machines on the morning of the 10th October for a short period which affected some of our Early Bird customers and meant that some PCNs were incorrectly issued.
"We had already approved all the customers who appealed to us about this situation and apologise for the inconvenience that this caused."