Supermarkets are struggling to meet demand for brand label milk as shoppers strip shelves bare in a show of support for farmers.

Dairy farmers have complained of falling prices since Coles and then Woolworths introduced $1-a-litre home brand milk five years ago.

But their plight was brought into sharp focus this month when Australia's two biggest dairy processors slashed the amount they would pay farmers for milk in the face of falling global prices.

A social media campaign has sprung up in response, calling for consumers to support farmers by buying more milk, cheese and yoghurt and asking them to choose branded products instead of supermarket's home brand goods.

Shoppers appear to have taken to the cause in droves, with widespread reports of Coles and Woolworths running out of brand-label milk.

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"Time to restock the Farmer Branded milks Coles?" one shopper posted on Coles' Facebook page on Tuesday with a photo of empty shelves in the dairy aisle.

Woolworths customers made similar complaints along with photos of empty shelves.

Woolworths said it had felt the affects of the campaign, which was given significant boost with a viral "call to arms" on television show The Project, experiencing a "noticeable increase" in demand for branded milk in the past few days.

"We are working together with our suppliers to respond to that change in customer demand as quickly as possible given our customers' desire for choice," a Woolworths spokesman said. Coles said it did not comment on sales figures. 

Australian Dairy Farmers president Simone Jolliffe said she did not encourage anyone to boycott certain brands, but did want to see people choose branded products.

"We always urge people to buy branded products where possible as this has an important flow on effect by putting more money back into the supply chain," she said.

"If consumers can't buy branded dairy products, just increasing consumption of Australian-made dairy will help."

While cartons of milk have been at the centre of the consumer push, only about a quarter of Australian milk ends up being bottled for drinking, according to Dairy Australia.

Rather, it's mostly turned into cheese (31 per cent) or milk powder (27 per cent), while 34 per cent of all milk produced is exported.

Coles was battling angry customers on two fronts on Tuesday, after a typo suggested its milk was made from reconstituted milk powder.