Inteferes with the packers (7)

I believe the answer is:

tampers

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'packers' is the definition.
Although both the answer and definition are plural nouns, I don't understand how they can define each other.

I don't understand the rest of the clue.

Can you help me to learn more?

(Other definitions for tampers that I've seen before include "Interferes with, meddles" , "Interferes with and damages" .)

I've seen this clue in the Sydney Morning Herald.

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