Walmart, the largest private employer in the U.S., said Tuesday it will extend health-care benefits to workers' same-sex partners starting January 1, setting a delayed example for other giant companies.

The change follows a United States Supreme Court decision in June to overturn the Defense of Marriage Act, which excluded same-sex couples from federal benefits received by heterosexual couples. The federal government must now provide benefits to same-sex couples in states where their unions are recognized.

Citing the DOMA decision, Walmart's memo to employees said, "By developing a single definition for all Walmart associates in the U.S. and Puerto Rico, we are able to ensure consistency for associates across our markets."

"[This is] a business decision, not a moral or political decision," it added.

With about 1.3 million workers, about half of whom have health insurance, Walmart's move puts pressure on other hold-outs. After years of opposing such a change, Walmart's new decision "may help tip the balance at companies such as trucker YRC Worldwide Inc. (YRCW), which is considering partner benefits for 2014, or Exxon Mobile Corp. (XOM), one of the biggest firms left without such coverage," say Bloomberg's Renee Dudley and Chris Burritt.

The Human Rights Campaign, a gay advocacy group, gave Exxon, which employs about 76,900 people, the lowest score for the group's Corporate Equality Index, which measures how policies affect gay, lesbian, bisexual, and transgender workers.

Exxon says it offers coverage for "legally recognized spousal relationships." A company spokesperson told Bloomberg, "We follow the federal definition of spousal relationships" in the U.S.

But Walmart might be too late to the game to have any real sway. It's hardly leading the way, says Andrew Belonsky at Out:

Sixty-two percent of Fortune 500 companies already have same-sex benefits. This is just Walmart making a symbolic business decision under political pressure, a decision that earns them lots of good will but may ultimately hurt its employees in the long run. If Walmart really cares about same-sex couples, they would lend their weight to the ongoing battle for full equality, which they have not. In fact, Walmart CEO Mike Duke has done the opposite: he signed a 2008 petition to stop same-sex adoption in Arkansas. [Out]

Others who support the most recent decision say it doesn't address an underlying problem with Walmart's health coverage. "The truth is a lot of associates who work at Walmart don’t have health care because they can’t afford it," said a member of OUR Walmart, a group trying to improve labor conditions.