Wal-Mart Stores Inc's U.S. employees will pay between 8 and 36 percent more in premiums for medical coverage in 2013, and now some of the 1.4 million workers at the nation's largest private employer say they will forgo coverage altogether.

In mailings sent to employees for its recently completed open-enrollment period, Wal-Mart noted that its rates would increase because healthcare costs continue to rise.

For its most popular plan, which covers individuals, the payment per bi-weekly paycheck is going up by $2, or 13 percent. Other plans will see larger increases as the world's largest retailer, known for low prices, tries to control its own costs.

Still, Wal-Mart said average costs its employees will bear should only rise about 4.4 percent in 2013, due to the elimination of some high premium plans, its move to offer free heart and spine surgery to most employees at six health care centers, and provision of other services, such as access to a healthcare adviser. That is less than the 9 percent average increase expected for all American workers next year, according to a study by human resources firm Aon Hewitt, though it isn't clear whether the figures are comparable.

Wal-Mart's example could be a blueprint for other employers trying to manage their costs while also preparing to meet the requirements of President Barack Obama's 2010 Affordable Care Act.

The law, the biggest reform to America's healthcare in decades, is intended to make healthcare less expensive but critics question whether it will succeed. It will also take years to fully implement. In the meantime, Wal-Mart and other large companies are trying to control their healthcare costs, which have been rising an average of more than 6 percent per year.

Wal-Mart pays for preventive care such as routine checkups. However, workers must pay deductibles of at least $1,750 before Wal-Mart covers 80 percent of the cost of other care such as doctor visits and diagnostic tests.

The retailer will also defray some costs with a separate contribution of $250 or $500 for individuals, and double that range for families.

Some workers say the price hikes for next year have pushed them to drop coverage.

"I really can't even afford it now so for it to go up even a dollar for me is a stretch," said Colby Harris, who said he makes $8.90 per hour and takes home less than $20,000 per year working in Wal-Mart's produce department in Lancaster, Texas.

Harris, a 22-year-old smoker, was set to see his cost per paycheck rise to $29.60 from $25.40. He says he has decided not to sign up for coverage.

More than half of Wal-Mart's U.S. employees sign up for its healthcare plans, which cover 1.1 million people, including dependents. Store workers across the country are offered the same plans as executives back at Wal-Mart's headquarters in Bentonville, Arkansas.

"Over the past few years we've all seen the cost of health care continue to rise nationwide, and 2013 is no different," Wal-Mart said in a statement. "As a result, we are adjusting rates for some of our health care plan choices. We are doing our best to keep health care costs as low as possible for our associates."

Barbara Andridge, who works at the Wal-Mart in Placerville, California, decided to drop out of a Wal-Mart plan provided for the retailer by a health management organization when she found out that the cost was set to nearly double to $60 a month.

"Sixty dollars isn't a lot to some people but when I have to think about buying winter clothes for my kids or sending my daughter to college I have to think of what is best for my children," she said. "Hopefully I'm making the right decision."

Andridge, who makes $12.05 an hour and said her husband was laid off this year, knows that she would have had to pay the same $60 monthly premium no matter how many hours she worked.

"Living paycheck to paycheck, I made the decision to swallow my pride and go and get county health," she said in reference to Medi-Cal, California's Medicaid health care program.

Wal-Mart has been touting its efforts to improve healthcare for its employees, including its October announcement that it would cover all costs, including travel, for costly, complicated heart and spine surgery at the six centers.

Nearly two-thirds of Wal-Mart employees sign up to cover only themselves. Rates covering individuals will rise $2 to $11 per paycheck, or 13 percent to 23 percent, according to documents viewed by Reuters. When plans covering families are included, rates rise anywhere from 8 to 36 percent.

Wal-Mart does offer some plans with premiums that are well below the national average.

Wal-Mart's lowest-cost and most popular associate-only medical plan will cost $17.40 per two-week pay period in 2013, up $2 from 2012. Costs for a single non-tobacco-using employee range from that to $59.30 per paycheck for 2013 (or $34.80 to $118.60 every four weeks).

According to the Kaiser Family Foundation's 2012 survey, the average monthly U.S. worker contribution this year was $79 per month for single coverage.

U.S. premiums are expected to rise 6.3 percent on average in 2013, human resources firm Aon Hewitt said in October, but premiums are just part of the costs story.

Newly hired part-time employees at Wal-Mart will have to work a minimum of 30 hours a week, up from 24 hours previously, before they qualify for coverage. The Affordable Care Act only requires larger employers to provide coverage for their staff who work at least 30 hours per week.

Other changes to Wal-Mart's 2013 plans, such as raising premiums, would have happened regardless of health reform, as it tries to control rising healthcare costs, the company said.

Harris and Andridge, who are dropping their coverage, are part of a group called OUR Walmart. Higher healthcare costs are one of the issues the group wants Wal-Mart to address, along with concerns such as wages and scheduling.

"Even if the plan only went up, let's say 50 cents, when you're barely making it every literal cent counts," said Harris.

OUR Walmart, which is not a labor union, is backed by the United Food and Commercial Workers International union, which represents workers at major grocery chains that compete with Wal-Mart. Members of OUR Walmart pay the organization dues of $5 per month.

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