Flagged laws will force up prices: Labor

Federal Labor has leapt on comments by Deputy Prime Minister Barnaby Joyce which suggest a change in competition law could push up the price of milk.

Mr Joyce has accused the major supermarkets of aggressively discounting the price of milk to lure shoppers away from smaller businesses.

Opposition agriculture spokesman Joel Fitzgibbon, who has been studying competition issues for years, told reporters in Canberra on Friday: "The loonies have taken over the asylum ... this (the change) will force consumer prices up."

Nationals deputy leader Fiona Nash took aim at Labor's support for big business.

"A market cannot function properly if big business is allowed to abuse its market power," she said.

"It will be interesting to see what blue-collar workers and unions think of Labor being in the pocket of big business."