A union appeal has put the decision to halve the minimum shift length for high school retail workers on hold for now.

The Shop, Distributive and Allied Employees Association were granted the right to appeal against Fair Work Australia's decision to allow high school students to work 90 minute shifts.

The decision was due to come into effect from tomorrow. The Australian Retailers Association's Russel Zimmerman told ABC News that retailers are outraged at the hold up.

"We've had a number of retailers telling us how great it was, that [now] the decision had been made they could employ students for one-and-a-half hours," he said. "So I think the retailers will feel this, they will feel that they are being unjustly treated."

The decision was made following a long-running battle by employers to have the previous minimum start of three hours reduced. Secretary of the Australian Council of Trade Unions, Jeff Lawrence, criticised the decision last week, saying it could impact on other workers.

"We've got a range of concerns with it, and we're particularly concerned that it'll encourage employers to cut back on shifts for adult workers," he told ABC News. "It just opens up a gateway to exploitation.And it could mean that children have to work for 90 minutes just to earn 11 bucks - a wage that would barely cover the cost associated with getting to work for many children and their parents," he said.