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Wal-Mart Stores Inc., the largest private employer in the U.S., will offer health insurance benefits to same-sex partners of its domestic employees beginning next year.

"Full-time associates can now cover any spouse or domestic partner of the same sex or opposite sex," Brooke Buchanan, a spokesperson for Wal-Mart told ABC News.

Employees in the U.S. and Puerto Rico were notified through a post card mailed on Monday detailing new additions to the benefits now available to them. Other benefits now include a new vision plan, which was not previously available, and the lowest medical premium increases in years, according to Buchanan.

"We believe this is a way to be consistent for our associates," Buchanan said. "We will offer the same access to benefits for all our associates across the 50 states and Puerto Rico." The company employs 1.3 million people in the U.S. and Puerto Rico, Buchanan said.

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To qualify for Wal-Mart's benefits, employees and their domestic partners must live together in an exclusive, non-committed relationship for 12 months with the intention to live together indefinitely, Buchanan said.

Both partners must not be related in any manner that would bar legal marriage in the state of which they live, meet the age range for marriage in their state of domicile, and must not be in a relationship for the sake of gaining coverage, she added.

"This is an opportunity for us to remain competitive in terms of attracting great talent for our company," Buchanan said.

Employees can begin enrolling for the new, broader package on Oct. 12, 2013 until Nov. 1, 2013.

The U.S. Supreme Court in June ruled that the federal government must recognize same-sex marriages in states where it is legal.

Wal-Mart's U.S. employees will pay 3 percent to 10 percent more for their medical coverage next year, depending on the plan, Reuters reported. The lowest-priced plan will cost $18.40 per bi-weekly pay period next year, up 5.7 percent.