Foodstuffs is again trying to bring its North and South Island operations under one roof, after failing two years ago.
The company's heading to the High Court to appeal a 2024 Commerce Commission decision blocking its plan.
Grocery Action Group chair, Sue Chetwin, says letting it do so would only strengthen the duopoly.
She says upstream, suppliers would have less choice on whom they could sell goods.
"So at the moment, they've got the North Island and the South Island Foodstuffs and Woolworths - but if you merged the North and South Island Foodstuffs, you'd be down to two."
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