Tell? Not if I have a say! (6)
I believe the answer is:
notify
'tell?' is the definition.
(I've seen this before)
'not if i have a say' is the wordplay.
I cannot really see how this works, but
'not' could be 'no' (negative) and 'no' is present in the answer.
'if' is within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for notify that I've seen before include "No one" , "Formally advise" , "Make known" , "Declare" , "'Advise, tell about (6)'" .)