Local and national organisations are campaigning to stop the Ministry of Defence from deregistering a vast area of land in Cumbria.
The commons are to the north-east of Appleby-in-Westmorland, in the North Pennines Area of Outstanding Natural Beauty.
If the land is deregistered it will bring an end to 'hundreds of years of tradition' within the farming community.
"When the MoD negotiated the buy-out and extinguishment of the commoner's grazing rights, one of the fundamental issues was MoD's agreement to leave the fells on the commons register," said William Patterson of the Hilton Commoners' Association.
"On the strength of this undertaking, the commoners' accepted the buy-out.
"It is a breach of trust that the MoD now wants to cancel that undertaking without making a further agreement. I believe that to safeguard the future of these fells the land must remain on the commons register."
Julia Aglionby, also of the foundation, said common land is the most valuable and protected type of land in England.
"The MoD's arguments for deregistering 11,000 acres of commons at Warcop are spurious, legally contestable and not in the national interest."
