Romuald Schaber, leader of the BDM German association of 30,000 dairy-cattle farmers, said the group expected the boycott to last between a week and 10 days.
He asserted that participation was "overwhelming" with 80 per cent of farmers taking part "in some regions." The unsold milk is being fed to calves or dumped in farm-waste tanks.
The farmers are angry at EU plans to increase output quotas and depress the market price of milk in the European Union. Brussels says it must respond to growing global demand for milk, especially from booming Asian nations.
But Schaber advised hospitals and retirement homes to stockpile milk before shortages began.
"All we can do now is use our milk as a weapon," he said. "Milk is might, and we have the milk."
The BDM said a farm gate price of less than 40 euro cents per liter for milk was uneconomic.
Germany's dairy farms are controlled by a few powerful companies which currently pay 27 cents a liter in northern Germany and 35 cents a liter in southern Germany for milk, according to BDM data.