A supermarket action group is questioning the Commerce Commission's decision making.

The Commission's decided not to investigate Sanitarium's move to pause the Warehouse's Weet-Bix supply, finding no evidence of anti-competitiveness.

Sanitarium paused supply after the Warehouse began selling the cereal more cheaply than major supermarkets.

Grocery Action Group's Ernie Newman says the Warehouse has had one issue after another, since it began selling groceries.

"People really did say- hey, we know when something is not fair play. But it seems that the Commerce Commission doesn't know when something is not fair play, and has simply fumbled this one."

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