Hundreds of Sheffield motorists were sent ‘threatening’ letters falsely accusing them of failing to pay parking fines.
Sheffield Council has apologised for the blunder, which was due to a computer error.
Figures show 700 motorists who had paid penalty charge notices were ‘mis-recorded’ as still having outstanding fines.
Records have been obtained for the six months from December 2012 to May this year.
The affected motorists received penalty charge notices for parking offences, driving in bus lanes or through bus or tram gates.
Letters asked for £90 - even though the maximum motoring fine is £60 - and said people who did not pay could have bailiffs sent.
The figures were obtained by the opposition Liberal Democrat group on Sheffield Council.
Coun Ian Auckland, Liberal Democrat spokesman for transport, said: “Receiving threats of bailiffs from the council is a pretty unpleasant experience for anyone.
“Moreover, motorists have been unable to get through on the phone to protest their innocence, being met with an answerphone message instead.”
Coun Auckland added: “I know Labour councillors are always attempting to squeeze more money out of local motorists, but attempting to, in effect, bully local people into paying twice is unacceptable.
“Labour bosses, who are responsible for another fine mess, need to apologise to those who have been affected.”
There were 102 cases in December, 77 in January, 220 in February, 119 in March, 128 in April and 54 in May.
Sheffield Council has already come under fire from motorists over the amount of money it makes from bus gate fines - branded ‘a licence to print money’.
In March, The Star revealed the Wicker bus gate made £440,000 after more than 7,000 motorists were snapped by enforcement cameras in the 12 months to February this year.
Sheffield Council said bailiffs have not been called to any addresses and the problem has been resolved.
A spokeswoman said: “This issue occurred due to the fact that some Bus Lane Penalty Charge payments were incorrectly allocated to council tax by the income management system, due to similar reference numbers, even though the council’s Parking Charge Notices are prefixed by “FD”.
The income management system collects the payments from the various sources - internet, phone payments, post office, paypoint - and distribute the payments to the various systems but there was a software problem in that it directed some bus lane payments into council tax.
The fact that the payments were misdirected resulted in the issue of charge certificates which requested payment of £90 (The original penalty charge notice being £60, or if they paid within 14 days of receipt the fine was £30).
“Charge Certificates do warn that if payment is not received the debt will be registered at the County Court and a warrant may be issued to a bailiff. However, none of these cases have been issued to bailiffs, as the payments have now all been applied correctly.”
Coun Bryan Lodge, cabinet member for finance, said: “Obviously, we apologise to all of the people who were affected by this problem and for any distress that it might have caused. Thank you to those people who brought this problem to our attention.
“We know that Capita, our IT Services contractor, have now re-directed the incorrect payments and they are making sure that all payments from mid-May are being directed to the right place within the system.
“In addition, we can assure people affected that no-one has been referred to bailiffs as a result of these errors. We are taking this situation very seriously and even with these assurances from Capita, we will be having discussions with them to make sure that we are satisfied that something like this doesn’t happen again.”