Morrison goes easy on SA state bank levy

South Australia's decision to issue its own levy on banks raises some reasonable questions, the federal treasurer has said.

Scott Morrison said it was up to South Australian Treasurer Tom Koutsantonis to explain the legality of the measures and how they sit with earlier GST arrangements, where states agreed to get rid of taxes in return for GST revenue.

"It raises a lot of issues but they're issues for the South Australian government to explain given they're the ones who've put it up," Mr Morrison told reporters in Sydney on Saturday.