A law that came into force 775 years ago could stand in the way of plans to move the City of London wholesale markets to Dagenham.
The Royal Charter, granted by King Henry III in 1247, bans a market from being set up within a day's sheep drive (6.66 miles) from Romford Market.
Havering Council could enforce the medieval law over concerns about retail trade at the relocated markets.
The markets will need Parliamentary approval to move to Dagenham.
The City of London deposited a Private Bill to Parliament last November for approval to move Smithfield and Billingsgate markets to Dagenham Dock.
While the bill was in its petitioning period, Havering Council submitted an objection based on the Royal Charter that founded Romford Market over 700 years ago.
The Charter stipulates that no other market can be set up within the distance a sheep can walk in a day from Romford Market - approximately 6.66 miles (10.7 km).
Havering Council does not always enforce the Charter on other markets in the area - but it is concerned about how the relocation of the City markets will affect local trade, especially if they are allowed to sell at retail to individuals.
Ray Morgon, leader of Havering Council, said that while the council supported the wholesale markets moving to Dagenham, the issue of retail trade had not been written into the bill.
"By Royal Charter of 1247, Romford Market is the only retail market allowed to operate within six and two-thirds miles, and this relocation could cause a potential loss in trade and business to our historic market," he said.
"Whilst we welcome the move, we ask that the bill be redrafted to restrict the relocated markets to wholesale-exclusive trade. We will be happy to discuss the licensing of any retail on site in the same way that we do for other local markets."
In response to the potential objection from Havering, a City of London Corporation spokesperson said: "We believe that the co-location is the best way of securing the long-term future of the markets, providing market tenants with room for growth and modern, environmentally sustainable facilities fit for the 21st century, while stimulating economic growth in Barking and Dagenham."
The petitioning period for the bill has ended and it is still under review in the House of Commons.