A grocery commentator says the markup on food products reveals the power supermarket giants have over shoppers

The Commerce Commission's first annual grocery report says supermarkets had up to 20-percent margins on basic products like milk, bread and eggs.

For chilled and frozen goods, snacks and liquor, it was more than 13-percent.

Ernie Newman says its an indication of market failure and requires intervention.

He says it will take political will to force a break up, and change the market back to operating competitively.