World Vision, the international Christian-based aid organization, on Monday made a surprise announcement on one of the most divisive social issues of the day, saying it will now employ Christians in the U.S. who are in legal same-sex marriages.

The Federal Way-based humanitarian group delivered the news to employees in a letter from President Richard Stearns.

Calling gay marriage one of the stormiest issues that has divided denominations, congregations and families, Stearns said leaders “wanted to prevent this divisive issue from tearing World Vision apart and potentially crippling our ability to accomplish our vital kingdom mission of loving and serving the poorest of the poor in the name of Christ.”

The company said its employee-conduct policy has been updated to reflect the change, which comes more than a year after a majority of Washington­ians voted to legalize same-sex marriages, now legal in 17 states and the District of Columbia.

The decision, first announced on the website Christianity Today, followed years of prayer and discussion by the board, he said, and added that it in no way suggests an endorsement of same-sex marriage.

World Vision continues to affirm “traditional” marriage as a God-ordained institution, Stearns wrote, but added that leaders also recognize that many of the 50-plus denominations his employees are part of have sanctioned same-sex marriage in recent years.

He said he is not bowing to outside lobbying or any concerns about government funding, but on this divisive issue is choosing to defer to “the authority of local churches” that have been struggling with this issue for some time.

“I want to reassure you that we are not sliding down some slippery slope of compromise, nor are we diminishing the authority of Scripture in our work,” Stearns wrote.

With more than $1 billion in revenue, World Vision is the largest global Christian relief organization, with more than 40,000 employees in 100 countries, including about 1,200 in the U.S.

More than 15 percent of its employees worldwide are not Christian, though all its U.S. employees are, and they are required upon employment to sign a statement of faith affirming that they believe in the deity of Jesus Christ and the Trinity.

Stearns said the organization will continue to require that statement from all employees and to expect abstinence before marriage and fidelity within marriage for all staff members.

The announcement comes as gay-rights advocates across the country continue to gain substantial ground on same-sex marriage and as religious organizations struggle with how to reconcile the apparent conflict with their teachings.

Fourteen federal courts have struck down anti-gay-marriage laws since the U.S. Supreme Court last year ruled that federal agencies cannot deny benefits to people in same-sex unions.

Information from The Seattle Times archives was used in this report. Lornet Turnbull: 206-464-2420 or lturnbull@seattletimes.com. On Twitter @turnbullL.