Councils will be given more powers to seize land under new plans by the government to boost housebuilding and critical national infrastructure.
The measure is part of Labour's flagship Planning and Infrastructure Bill, which has now been introduced in parliament to help build 1.5m new homes over the next five years.
Housing Minister Matthew Pennycook said the government wanted to make use of compulsory purchase orders more often, which permit authorities to acquire land without the consent of the owner.
Currently, local authorities purchasing sites via compulsory purchases must factor in the "hope value", which is the potential value if planning permission for development is secured.
This is set to be axed to allow land to be bought at a lower price, but farm leaders have raised concerns that farming businesses could be forced to sell at poor prices.
The NFU said farmers and landowners "must be fully consulted every step of the way" amid fears that farmland could be more frequently targeted by compulsory purchases.
The union's vice president, Rachel Hallos said: “The housing minister told media that these new powers would be used to access brownfield and urban land, and that must be the case.
"Anything else further undermines the government’s policy that food security is national security."
She added: "UK food security and the protection of our environment has rarely been more vital, and productive farmland needs securing for our collective future more than ever.
"However, giving authorities more power to acquire land through compulsory purchase and process of using directions to remove ‘hope value’ will need to be thought through carefully to ensure farmers are compensated fairly.”
Country Land and Business Association (CLA) deputy president, Gavin Lane added that pushing farmers and landowners into selling land "isn’t the answer".
"Compulsory purchase drags landowners through years of stress, disruption and compensation battles, harming individuals and communities alike.
“Instead of pushing landowners to bear the burden, why not work with them? Most want to see progress and could deliver development faster, cheaper and with more care."
He concluded: "Hitting landowners isn’t the solution – fixing the planning system is."
