Labor tried to force a vote requiring the competition watchdog to investigate setting a minimum price on milk, but it was voted down.

Opposition agriculture spokesman Joel Fitzgibbon wanted the Australian Competition and Consumer Commission to test how a minimum farm gate milk price would work to protect the struggling dairy industry.

"Our farmers aren't making money, most are losing money," Mr Fitzgibbon told parliament on Wednesday.

"The great ironic part of the market is our retailers aren't making money either, but in this case because they choose not to."

But the vote was lost 69 to 74, as Agriculture Minister David Littleproud said pushing for a minimum price was an outdated stunt.

"That would be taking us back to a regulated marketplace," he told reporters.

"We've got in place trade agreements that have helped take the agriculture industry over the last eight years from around $34 billion to $60 billion.

"We've got to do more work on those trade agreements to get better access for dairy in particular, but to go back in time is not going to help."

Mr Littleproud said he was taking steps with the industry to create a mandatory code of conduct, which is due to begin by mid-2020.

Labor is also promising to establish a mandatory dairy code of conduct to ensure the market is functioning fairly for all participants.

Woolworths stopped selling its home-brand milk at $1 a litre on Tuesday, upping the price by 10 cents with the extra money to go back to farmers.

But Coles said it would not axe its $1-a-litre Coles-branded milk, citing cost of living pressures on customers.

Aldi said low prices were a core promise to its customers, and it did not support retailer-led initiatives seeking to bypass the normal supply chain.

Mr Littleproud on Tuesday accused Coles of pretending to be a decent corporate citizen and Aldi of "hiding under the stairs" after they failed to follow Woolworths.

He said the price war that began eight years ago had been a disaster for farmers.

Australian Associated Press