Union breaking up companies? It's just the opposite (8)

'the opposite' is the definition.
I know nothing about this answer so I cannot tell whether it can be defined by this definition.

'union breaking up companies? it's' is the wordplay.
I cannot quite see how this works, but
'union' could be 'merger' (merger is a kind of union) and 'merger' is found in the answer.
'it' could be 'e' ('e' can mean 'electronic' which is similar to 'IT') and 'e' is present in the answer.
A single letter 'd' remains which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).

'just' is the link.

Can you help me to learn more?