Dairy farmers have been protesting at Number 10 Downing Street over low levels of milk prices.
Protesters wore their cow costumes to Downing Street
A group of Devon farmers handed in a 3,000-signature petition demanding an inquiry into supermarket milk prices.
Neil Parish, chairman of the European Parliament's agriculture committee, said urgent action was needed to give milk farmers fairer prices.
Recent National Farmers' Union figures showed English and Welsh dairy farmers were making annual losses of £270m.
A group of Devon Young Farmers, who call themselves "The Great Milk Robbery", have been protesting by dressing up as cows and collecting petitions at supermarkets across the South West.
On Tuesday - dressed in their cow costumes - they handed in their petition to 10 Downing Street.
Mr Parish, the Conservative MEP for the South West region and a former dairy farmer himself, said: "Farmers are presenting a serious grievance to the government."
"This is not a case of farmers crying over spilt milk.
"We get paid the lowest price for our milk amongst the major producers in Europe."
Mr Parish said many dairy farmers believe supermarkets were "illegitimately using their buying clout to force prices lower than farmers can sustain".
But UK supermarket giant Tesco responded by saying: "We understand the concerns of farmers but we purchase from processors and not direct from suppliers.
"We think the most helpful thing we can do as a retailer is to continue to work with the supply chain to grow the amount of UK dairy products that are sold and to develop new opportunities."