Scottish Green MSPs have joined in a call for supermarket chain Tesco to pay a "fair price" for dairy milk.
Farmers have been calling for a "fair price"
Green MSPs Chris Ballance and Eleanor Scott were distributing postcards on Saturday urging Tesco to pay farmers a larger share of the retail price.
Former dairy farmer John Sherrell said the supermarket chain had a duty to "do right" by food producers.
However, Tesco said it was a "strong supporter" of the milk industry and wants a sustainable future for farmers.
The protest forms part of a national campaign by pressure group Farm.
Farm, an independent organisation which represents farmers, said it wants to halt the decline in small dairy farms.
Mr Ballance, MSP for South Scotland, joined campaigners at a Tesco store in Dumfries, while Ms Scott, MSP for Highlands and Islands, campaigned in Inverness.
She said: "Consumers should be aware that supermarkets are paying very low prices for milk and are driving dairy farmers out of business. Most supermarkets nowadays stock fairly traded coffee and chocolate.
"We want fair trade for farmers here in Scotland, as well as for producers in developing countries. By not giving local producers a fair deal, supermarkets are driving the farming industry in this country into crisis."
John Sherrell, a former dairy farmer and member of the Farm campaign group, added: "Tesco is immensely profitable - it is said to get one in £8 spent by UK shoppers. With this power comes a responsibility to do right by the food producers on whom its profits are based."
Tesco said it was "one step removed" from the relationship between farmers and their processors.
A spokeswoman said: "Tesco is British agriculture's number one customer and a strong supporter of the UK milk industry.
"Our aim is to work with our suppliers to create sustainable relationships with dairy farmers.
"We believe the most positive thing we can do is to continue to work with the supply chain to grow the amount of UK dairy products that we sell and develop new opportunities."
On Thursday, more than 250 protesting dairy farmers stopped delivery trucks from getting into Asda's distribution depot in Falkirk.
They have been angry over the supermarket's pricing policy, which they claim means farmers get paid less for milk, despite price rises at checkouts.
The farmers have called on customers to shop elsewhere and have threatened to picket shop doors.
Asda said it had recently increased the amount it is paying producers.