Dozens of tractors circled Melton Mowbray to raise concerns over post-Brexit farming and food standards.
Farmers said they are worried ahead of the EU transition period ending.
An Agriculture Bill will return to the House of Commons next week after a House of Lords session this month.
The Department for Environment, Food and Rural Affairs said it "will not compromise on our high environmental protection, animal welfare and food standards".
"We are a world leader in these areas and that will not change," a spokesman said.
Steve Elnor, who runs a family farm near Grantham in Lincolnshire, said his business faces "a massive threat from the government's apparent determination to tear apart the USP of British food in order to strike trade deals in desperation", adding farmers "have the overwhelming support of the public".
"We are facing a revolution and I worry it is something that we, and many other family farms up and down the country, won't be able to adapt to," he said.
"We face uncertainty from 1 January, 2021, not knowing what the market and prices will be."
Lord Tyler, a Liberal Democrat peer on the House of Lords Agricultural Committee in Lords, said he backed efforts to "support British farmers and protect our food supplies from adulterated and expensive imports".