WA Premier Colin Barnett has demanded Labor submit its election promises to Treasury for costing, saying that should be the modern standard for oppositions.

While oppositions have previously had accounting firms run the ruler over their pledges, Mr Barnett says that's not enough in the modern political arena.

Premier Colin Barnett and and Deputy Premier Liza Harvey on the campaign trail. Credit:Trevor Collens

"Those days are gone. It's a far more accountable, sophisticated process that we go through now," Mr Barnett told reporters on Wednesday.

"People used to say all sorts of things in election campaigns. We've moved on."