Car parking spaces that are adjacent to walls, fences, and obstructions should be made 0.3m wider than the standard width to account for car door opening.
If your garage spaces have been designed with no additional allocation for obstructions then no obstructions should be permitted.
Below is an article regarding design considerations for building developments
https://www.cityofsydney.nsw.gov.au/__data/assets/pdf_file/0004/119632/DCP11_Section4.pdf