Steep service charge applied to staff (8)
I believe the answer is:
macerate
'steep' is the definition.
(thesaurus)
'service charge applied to staff' is the wordplay.
'service charge' becomes 'rate'.
'applied to' means one lot of letters go next to another.
'staff' becomes 'mace' (mace is a kind of staff).
'rate' after 'mace' is 'MACERATE'.
(Other definitions for macerate that I've seen before include "Steep in liquid like cream tea" , "Soak" , "Cream tea (anag) -- soften by steeping in liquid" , "Soften food by soaking" .)