"Parent Free" teen events

Hi all
I am a youth services librarian at a fairly small library. Our teen program policy is that teen events are "parent free" to give the teens a chance to have some space that is just for them. However, I keep running into problems with parents who are VERY against this policy and want to be able to sit in the space with the teens and just.....watch? idk, it's frustrating for me. I keep getting push back from what I would describe as "helicopter parents". Has anyone else run into this problem?