Sacked, if turning communist (5)
I believe the answer is:
fired
'sacked' is the definition.
(both can mean dismissed from a job)
'if turning communist' is the wordplay.
'turning' shows that the letters should be reversed in order.
'communist' becomes 'red' (red can informally mean communist).
'if' back-to-front is 'fi'.
'fi'+'red'='FIRED'
(Other definitions for fired that I've seen before include "Stimulated; dismissed" , "Discharged" , "Sacked or ignited" , "got rid of" , "with P45?" .)