The Commerce Commission's launched investigations into the two big supermarket chains' pricing and promotional practices.  

It's looking into whether the practices of Woolworths, Foodstuffs North Island and Foodstuffs South Island, comply with the Fair Trading Act.  

It comes following a Consumer NZ complaint to the commission, after it asked shoppers for examples of unclear or misleading prices. 

They offered 600 responses.  

Massey University marketing professor Bodo Lang told Roman Travers that the Commission's options range from a compliance letter to court proceedings with fines.  

He says a charge is really just a signal but consumers would react negatively, leading to changes in practices. 

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