Such a non-negotiable issue visibly embarrassed business

I believe the answer is:

red line

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'such a non-negotiable' is the definition.
I can't tell whether this definition defines the answer.

'visibly embarrassed business' is the wordplay.
'visibly embarrassed' becomes 'red'.
'business' becomes 'line' (line is a kind of business).
'red'+'line'='RED LINE'

'issue' acts as a link.

Can you help me to learn more?

(Other definitions for red line that I've seen before include "Limit beyond which a party will not go in negotiations" , "Cancel" .)

I've seen this clue in The Telegraph.

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