The state campaign finance board decided Friday that a marriage amendment contributor who works for a Catholic organization can remain anonymous out of fear that disclosure of his donation to a group opposing the measure could cost him his job.

A man known only as "John Doe" had contributed $600 to Minnesotans United for All Families last year, but requested anonymity.

"Doe" told the board he must represent the Catholic organization's policies to the public and knowledge of his opposition to the marriage amendment "would cause immense strain in his working relationships" and "may be enough that his employment would be terminated."

Gary Goldsmith, executive director of the Minnesota Campaign Finance and Public Disclosure Board, said it was the first time a political contributor asked to remain anonymous. The ruling highlights the strong feelings the amendment raises statewide, along with the deep divide within the Catholic church, the state's largest denomination.

Minnesota law allows exemptions from the requirement to disclose the names and employers of contributors if it would cause specific harm. "In this matter, the board concludes that this requirement has been met," the board ruled.

Church leaders have firmly backed the proposed amendment, which goes before voters in November. The church has collected hundreds of thousands of dollars for the campaign and instructed clergy not to dissent from the church's position.

Marriage amendment supporters are asking voters to cement into the Constitution that marriage is a union between a man and a woman. State law already forbids same-sex marriage, but supporters worry that judges or future legislatures could change that.

It is not the first time activists have raised concerns about potential backlash for contributors. Marriage amendment supporters have told the board that some of their donors could face recriminations if their contributions were made public.

Minnesota for Marriage spokesman Chuck Darrell underscored that fear in reaction to the board's decision, which he dismissed as "political."

"[The] history of donor harassment on the marriage issue overwhelmingly shows that it is only the donors to traditional marriage who are harassed," said Darrell, whose organization is the lead group supporting the amendment. "People contributing to or supporting pro-marriage campaigns have been shot ... fired, had their businesses attacked [and] been subjected to protests and boycotts."

The board has grappled with how to handle the request from "John Doe" since 2011. Since then, the source of the money has been lumped in with contributors who gave less than $100, who do not have to be identified.

Now, Minnesotans United for All Families, which has raised more than $4 million to fight the amendment, will disclose the contribution as being from "John Doe" without risk of penalty.

"We just think it's really sad that someone is afraid of losing their job because they don't want to limit the freedom to marry in Minnesota," said Kate Brickman, spokeswoman for Minnesotans United.

She said the board decision may give other Catholics encouragement to get involved.

Asked whether the anonymous donor's fears were justified or whether employees had been told not to make donations to groups opposing the amendment, Jim Accurso, spokesman for the Archdiocese of St. Paul and Minneapolis, shared little information.

"The Archdiocese of Saint Paul and Minneapolis does not comment on personnel matters, and is in the process of reviewing the information in today's order," he said in a statement.

In making its decision, the state campaign finance agency examined the case of Trish Cameron, a former teacher at St. Joseph's Catholic School in Moorhead. Cameron told agency officials she told her supervisors that she personally objected to the church's opposition to same-sex marriage. She said she disclosed the information during a private, annual self-evaluation and noted that she would not bring her personal beliefs into the classroom.

"A week later," the campaign finance agency wrote, "Ms. Cameron was asked to resign."

Rachel E. Stassen-Berger Twitter: @rachelsb