Additional work due to unexpected item (8)
I believe the answer is:
overtime
'additional work' is the definition.
(work outside of contracted hours)
'due to unexpected item' is the wordplay.
'due to' becomes 'over' (as in quitting a job over an issue).
'unexpected' is an anagram indicator.
'item' is an anagram of 'time'.
'over'+'time'='OVERTIME'
(Other definitions for overtime that I've seen before include "Work in excess of fixed period" , "Extra hours (at work)" , "Work beyond normal hours? Remove it" , "Pay for extra work" , "Extra hours worked" .)