Residents are being asked not to visit Portsmouth City Council to make a payment on Wednesday 26 and Thursday 27 April.
The council is updating its computer system on those two days, and staff will be unable to process cash, cheque or card payments taken over the counter. The quick-pay machines in Civic Offices reception will also not be working.
Staff will also be unable to take card payments over the phone.
But on both days, payments will still be possible using this website, and the automated 24-hour payment line, 0800 876 6576.
A council spokesperson said: "We're sorry for any inconvenience while we improve our computer system. Residents can still make payments online and on the automated phone line, but we're asking them not to visit in person on those two days. We won't be able to process their payment in the normal way and we don't want anyone to have a wasted journey."