Legally I don’t see how anyone can take action against you for passing on information regarding action that people are taking that involves breaking bylaws (illegal parking). You are just informing the culprits that they are breaking the bylaws and advising them of what action can be taken against them if they persist.
I doubt these letters would be considered official notification but they would count if the issue went to CTTT and offenders claimed they didn’t know they were doing wrong.