I have parental responsibility for my son his father does not, is he allowed to cut his hair after I have asked him not to. I am worried that next time it could be something more serious like having his ears pierced. What can I do

Long jump from hair cut to ear pierced, how old is the child, did the child want a hair cut ?

Also not sure where you live, I know of physical and legal custody and other wording on medical and educational issues which parent has the final say ( unless it is required to go mediation)

I would say there are bigger issues than a hair cut please explain what is going on.

I doubt the court would do anything but laugh at you if you tried to go back to court over a hair cut ( and that is your only option take him back to court)