British farmers say cheaper New Zealand lamb is costing them about $55 (£29) for each animal they sell.
The National Sheep Association says supermarkets are opting for New Zealand meat imports over British lamb at a time when the country's sheep farmers are struggling.
The association says that is a bitter blow when farm gate prices have dropped by more than a fifth in the past year due to poor conditions and rising production costs.
Mike Thomas, a spokesperson for Britain's National Farmers Union, is calling on supermarkets to support the country's lamb sector over imports.
"We would obviously encourage the retailers to stock British lamb, but at the end of the day it's very much a retailer's own decision."
Mr Thomas says the union wants to know why farmers are being paid less, yet supermarket prices remain high and demand from consumers is strong.