A sign outside The Home Depot store is pictured in Monrovia, California in this August 13, 2012 file photo. REUTERS/Mario Anzuoni/Files

(Reuters) - Home Depot Inc is shifting medical coverage for part-time workers to new public marketplace exchanges ahead of new benefits requirements under the U.S. Affordable Care Act, a spokesman said on Thursday.

The world's largest home improvement retail chain announced its move shortly after a similar announcement from Trader Joe's Co, a popular privately held grocery chain.

Home Depot's change would affect roughly 20,000 part-time workers who previously had chosen the limited liability medical plan the company offered, spokesman Stephen Holmes said.

After December 31, companies can no longer offer those plans under the health law, also known as Obamacare.

"We're going to shift them over to the public exchanges, where there are more options," Holmes said.

The public exchanges being set up under the law will allow individuals to buy government-subsidized healthcare based on income. Enrollment begins on October 1.

Until now, many restaurants and retailers offered workers limited liability plans that often provided less than $5,000 in coverage.

Home Depot's plans for part-time workers provided coverage of up to $20,000 depending on the plan and were administered by Aetna Inc.

Experts have said exchanges would provide more comprehensive coverage that may not cost more because government tax credits will help some workers offset premiums.

Some employers are opting to offer coverage through private health insurance changes.

Walgreen Co, the largest U.S. drugstore, and more than a dozen other large employers have said they would offer their employee insurance for 2014 through the Aon Hewitt Corporate Health Exchange.

Home Depot employs about 340,000 people and will continue to offer healthcare benefits to full-time employees, who will be paying more for that coverage next year due to higher healthcare costs, Holmes said.

(Reporting by Lisa Baertlein in Los Angeles; Additional reporting by Phil Wahba; Editing by David Gregorio and Tim Dobbyn)