Global companies with a presence in Australia prevent local customers from taking advantage of cheaper prices offered on their overseas websites, consumer group Choice says.

In its submission to the Productivity Commission's retail inquiry, Choice says Australian retailers must explain why they charge huge mark-ups on products that cost half as much from overseas internet companies.

Australians are paying more for everything from computer games to motorcycles, Choice says.

A strong Australian dollar should enable local retailers to pass on savings to their customers, Choice said.

It has found that a pair of Nike running shoes costs $240 at a major Australian sports retailer while consumers can buy the same shoes for $134 from an online store based in the US.