Significant worker's sacked with obligation for tax (6,4)

I believe the answer is:

import duty

'tax' is the definition.
(I know that import duty is a type of duty)

'significant worker's sacked with obligation' is the wordplay.
I cannot quite see how this works, but
'obligation' could be 'duty' (synonyms) and 'duty' is located in the answer.
The remaining letters 'import' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...

'for' is the link.

I've seen this clue in The Guardian.

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