Firm legislator replacing a line in union agreement (10)
I believe the answer is:
compliance
'agreement' is the definition.
(compliance is a kind of agreement)
'firm legislator replacing a line in union' is the wordplay.
I cannot really understand how this works, but
'firm' could be 'co' (a firm is a company) and 'co' is found in the answer.
'legislator' could be 'mp' (an MP legislates in parliament) and 'mp' is found within the answer.
'a' could be 'an' and 'an' is located in the answer.
'line' could be 'l' (used when specifying particular lines from a poem) and 'l' is present in the answer.
The remaining letters 'ice' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for compliance that I've seen before include "submission" , "Agreement" , "submissiveness" , "deference" .)