Catering supplier the Burger Manufacturing Company (BMC) has withdrawn some of its products after samples tested by Powys County Council showed at least 1% horse meat.
The Food Standards Agency (FSA) said further work was being carried out to establish exactly how much horse meat these products contain and to test for the presence of the veterinary medicine phenylbutazone, or bute.
BMC, based in Builth Wells, Powys, is contacting its customers to inform them of the results of these tests and to withdraw any of the affected products that they may have.
On its website, the company claims to supply cafés, restaurants, hotels and leisure outlets with its steak burgers.
John Sparks, director of The Burger Manufacturing Company, said: "Following rigorous tests by Trading Standards, Environmental Health the Food Standards Agency (FSA), I can confirm that traces of horse meat have been found in some of our previous batches of burgers which are now being recalled and all customers affected have been contacted."
"Following a thorough investigation, we are confident that the meat can be traced back to our supply from Farmbox Meats Ltd. With immediate effect, we stopped using the supply to ensure that it did not enter any other products.
"This is an isolated incident. Our products regularly undergo rigorous tests from both and Internal and External Auditing procedure.
"We pride ourselves on using quality meat from, where possible, locally sourced suppliers. Our decision to use Farmbox Meats Ltd was to help boost local businesses, and because of our belief in the quality of their meat. It is disappointing that on this occasion the high standards we expect have not been met.
"We will be working rigorously to ensure that such instances do not happen again and we are now putting in place continued DNA testing across our products."