NEW YORK (CNN/Money) - McDonald's, the world's number one fast-food restaurant and second-largest buyer of chicken, is studying whether to switch its chicken suppliers over to the least-cruel slaughter method, the animal rights group PETA said Tuesday.

Controlled-atmosphere killing, or CAK, is a USDA-approved method of slaughter that is described by animal welfare experts as "the most stress-free, humane method of killing poultry ever developed." The CAK method puts the birds to sleep quickly and painlessly.

According to the animal-rights group, McDonald's (Research) said some of its EU suppliers are already using CAK technology and a feasibility study for the U.S. will be ready this summer. A PETA spokesperson said McDonald's is the first corporation to seriously consider CAK technology and they are hopeful that McDonald's will spur an industry-wide shift.

McDonald's is "committed to animal welfare leadership and to working with our suppliers and recognized experts on animal welfare issues" Anna Rozenich, a spokeswoman for the fast-food restaurateur, told CNN/Money.

According to PETA, chickens are currently exempt from animal cruelty laws and are routinely killed by shackling the birds upside down by their feet, slitting their throats and immersing them in boiling water, all while still alive.

News of McDonald's CAK study surfaced after PETA filed a shareholder proposal to require the company to study CAK and post the results on the company Web site. McDonalds said they were already studying CAK and agreed to the Web site request if PETA withdrew the proposal.

PETA agreed and results should be posted by June 2005.

In September 2000, PETA suspended its 11-month "McCruelty to Go" campaign against McDonald's in response to the fast-food chain's announcement that it would improve living conditions for its chickens.

PETA claims the 2000 campaign triggered McDonald's improvements, but McDonald's officials said PETA's campaign had nothing to do with its initiative to improve conditions for its laying hens. PETA "refused to have a constructive dialogue with McDonald's and our outstanding team of experts," the company said in a statement issued at the time.