Campaign group Farmers for Action (FFA) blocked the entrances to a Robert Wiseman dairy in Droitwich Spa, Worcestershire, and another plant at Folston in Derbyshire, the BBC reported.
FFA told the BBC that about 400 farmers and 20 tractors formed the blockade at the Folston site last night.
Dairy farmers are furious about cuts of up to 2p a litre in the amount they receive from major milk processors and many fear the shortfall will force them out of business.
The action is the latest in a series of protests by farmers who are angry that they are to be paid less for their milk than it costs to produce it.
Yesterday dairy farmers welcomed a move by the Co-operative Group to increase the premium it pays to its farmers for their milk.
The group said it would pay produces a total price of 29 per litre.
Steve Murrells, chief executive of Co-operative Food, said: "We have a track record of supporting British farmers, and we recognise the importance of ensuring a long-term, sustainable future for British dairy farmers.
"We are taking this action to help alleviate the immediate pressures that farmers within the Co-operative Dairy Group are facing."
Peter Kendall, president of the National Farmers Union, welcomed the move, but said other retailers needed to follow suit.
He said: "We are encouraged by the positive step taken by The Co-operative in ensuring that its farmers will be paid a fair price for their milk.
"Their recognition of the real difficulties being faced by British farmers this summer and commitment to support them through these difficult times is to be applauded.
"But whilst this is an important move, all retailers must move to a sustainable funding model for the dairy industry."