We object to long period in employment (5)
I believe the answer is:
usage
'employment' is the definition.
(I know that employment can be written as usage)
'we object to long period' is the wordplay.
'we object' becomes 'us' (object pronoun for 'we').
'to long period' becomes 'age' (I've seen this before).
'us'+'age'='USAGE'
'in' is the link.
(Other definitions for usage that I've seen before include "Common practice" , "Utilisation" , "Acceptable language" , "Silly little thing" , "Accepted or habitual practice" .)