Workers protected by a welcome understanding (9)
I believe the answer is:
agreement
'understanding' is the definition.
(I've seen this before)
'workers protected by a welcome' is the wordplay.
'workers' becomes 'men' (man is a kind of worker).
'protected by' is an insertion indicator.
'welcome' becomes 'greet' (I've seen this before).
'a'+'greet'='agreet'
'men' put into 'agreet' is 'AGREEMENT'.
(Other definitions for agreement that I've seen before include "Correspondence" , "consensus" , "Unlikely result" , "in sympathy" , "Compact, accord" .)