Work with iron causing distress (7)
I believe the answer is:
oppress
'distress' is the definition.
(I've seen this before)
'work with iron' is the wordplay.
'work' becomes 'op' (abbreviation for opus).
'with' means one lot of letters go next to another.
'iron' becomes 'press' (I've seen this in another clue).
'op'+'press'='OPPRESS'
'causing' acts as a link.
(Other definitions for oppress that I've seen before include "Subjugate by force" , "Torment" , "Distress" , "Subjugate or weigh on" , "Lie heavy upon" .)