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DreamWorks Heroes action cards featuring characters from movies such as Shrek, Kung Fu Panda and Madagascar are collected through a Countdown supermarket promotion.
They are popular with primary school pupils, who have been trading them in playgrounds in recent weeks.
But the schoolyard trading is starting to cause trouble, with some pupils pressuring others into unfair deals.
Arthur Street School principal Verity Harlick said she discouraged pupils from bringing the cards to school after some trades went ''awry''.
''We have requested that our children don't bring them to school, for their own peace of mind and safety.
''For us, it had been going quite smoothly. A lot of the children had bought the collector's book and they were trading and admiring the cards.
''But there had been a few unfair trades which had occurred.''
She said a couple of parents had asked the school to collect them back from pupils.
''Because some of the cards have a higher value or status than others, that was where the difficulty was coming in.''
Andersons Bay and Mornington Schools have also banned the cards.
Mornington School principal Brent Caldwell said a great deal of swapping had occurred in the playground, and they had also started to appear in lesson time.
''The supermarket promotion has a limited shelf life, and like most market-driven collectable crazes, it will soon pass.''
Mr Caldwell said it was one of many ''fads'' that went through schools, but one of only a few banned in recent years.
He said another recent craze - Rainbow Bands (coloured wristbands) - had been good for pupils because they had worked collectively to produce an ''amazing array'' of wristbands in vibrant colours.
Green Island School principal Steve Hayward said the cards had not been banned at his school yet, but he was monitoring the trading among pupils.
''We haven't banned them like we had to do with the old Pokemon cards in the past,'' Mr Hayward said.
''We banned those because kids were using standover tactics - there was unfair swapping, you know, that kind of stuff.
''At the moment, we haven't got any issues, but I'm not saying that won't happen in the future.''
Countdown Dunedin area manager Stuart Worsnop said there had been a great response to the cards in Dunedin and swap meets had been organised at stores around the country.
A swap meet would be held at Dunedin stores on Sunday to give children the opportunity to complete their sets, he said.
''The campaign runs until stocks last, which is expected to be the middle of June.''