Changing The Parking Signs Then Issuing A Fine

I have lived in the CBD for about 4 years. I've been using CBD Residential Parking during this period.

Last week I parked my car in an area designated for CBD Residential Parking. During the week they changed two spots in this area to a Work Zone. My car was parked in one of these spots.

When I parked my car, there was no signs indicating that they were going to change the parking zone. As a result, I was issued with two parking infringement notices.

Is the council allowed to change the parking zones without adequate notice and then issue fines?

If not, how do I go about having these parking infringes canceled.

• Sydney City Council
• Parking