Burger King is dumping thousands of beefburgers from the supplier at the centre of the horsemeat scandal - despite insisting its food was not contaminated.
Staff have been ordered to box up Whoppers and Angus burgers and ensure they are not sold to customers.
The fast-food giant was bitten by the controversy last week after tests showed the Silvercrest meat processing plant in Ireland and another site in Yorkshire had supplied burgers with traces of equine DNA to supermarkets.
Several supermarkets took burgers off the shelves, but Burger King said last Thursday it would not be following suit.
By the weekend its restaurant managers were being ordered to remove all Silvercrest burgers.
Burger King has now said it is switching to a different supplier for its British and Irish restaurants as a "voluntary and precautionary measure".
The ABP Food Group, one of Europe's biggest suppliers and processors, stopped work at its Silvercrest plant in Co Monaghan after new tests last week revealed contamination in frozen burgers.
But ABP has insisted that meat for Burger King was stored and processed separately and there is no evidence that its burgers are affected.
Burger King said the withdrawal could lead to shortages of burgers in its restaurants.
It said: "We apologise to our guests for any inconvenience. However, we want to let them know that they can trust us to serve only the highest quality products.
"We take this matter seriously and will continue with our investigations to determine how this situation occurred and what lessons can be learned."
Ten million burgers have been removed from supermarkets across Ireland and the UK as a result of the scandal.
Tesco took out full-page adverts in a number of newspapers apologising for selling the contaminated beefburgers, and Aldi, Lidl and Iceland also withdrew burgers after they were found to contain horsemeat, which is safely eaten by millions on the Continent.
Sainsbury's, Asda and the Co-op later withdrew some frozen products but stressed that the move was "purely precautionary" and they had not been found to be selling contaminated food.
Meanwhile, Labour has claimed a drug with the potential to cause cancer in humans might have entered the food chain through meat from horses slaughtered in UK abattoirs.
The anti-inflammatory drug, phenylbutazone, is banned from being allowed in the human food chain in the EU.
Labour's shadow environment secretary Mary Creagh told the Commons there was evidence the drug - also called Bute - was found in "several" horses slaughtered in the UK last year.
Britain's Food Standards Agency (FSA) said Bute was found in five cases during checks on slaughtered horses in 2012. None of the meat had been placed for sale in the UK and foreign safety authorities were informed, the FSA said.
The Food Safety Authority of Ireland has retested all burgers found to contain traces of horsemeat and all were negative for Bute.
Companies involved in the separate horsemeat scandal that emerged last week have blamed meat suppliers on the Continent rather than British abattoirs.