Executives at the fast food firm promptly dropped Sparboe Farms as a supplier, but the move is not enough for animal rights campaigners at Mercy For Animals, who are urging McDonald's heads to buy eggs from more humane sources.

The stars, along with comedian Steve-O, rocker Bryan Adams, actress Emily Deschanel and True Blood star Kristin Bauer, are among a group of 10 celebrities who have signed an open letter to McDonald's American CEO Jim Skinner calling for the company to follow in the footsteps of its European operation and ban eggs from caged birds.

The letter reads, "While McDonald's has already established a 100 per cent cage-free purchasing policy in Europe, your US restaurants continue to support egg factory farms that confine hens for most of their lives in cages so small they can't even spread their wings, nearly anything that comes naturally to them. Common sense tells us that animals with legs and wings should be given the basic freedom to move.

"Sadly, there is not a single federal law to protect hens from cruelty from the time they hatch to the time they are killed. While McDonald's brags about the 'billions and billions served', millions of hens exploited for your restaurants are being grossly underserved. In fact, these animals are being abused in ways that would land your egg suppliers in jail, if dogs or cats were the victims."