They are angry with the government heritage adviser for opposing redevelopment of the disused and unlisted General Market Building by Thornfield Properties.
The developer wants to build a seven-storey office, shop and restaurant scheme. It argues that the complex must be demolished because tunnels underneath it are beyond repair.
The butchers also accused English Heritage of drawing up secret plans to redevelop the entire market and remove them completely.
Urban designer Terry Farrell, who carried out a study of the area for the agency, published a masterplan for the site in September showing art galleries, workshops and restaurants.
Smithfield Market Tenants Association chairman Greg Lawrence complained: "English Heritage did not even have the courtesy to consult us at any point."
But English Heritage said it did not ask Farrell to produce a masterplan. It claimed that this is being used "to muddy the waters" by Thornfield's supporters.
"We are keen to see the building saved. The City of London has systematically neglected it and is effectively trying to offload the cost of tunnel repairs onto a developer," said a spokeswoman.
Developers such as Urban Space Management, Add Leisure and Can Mezzanine are interested in redeveloping it, she added.