Marcello Araujo was once a rising star at Jews for Jesus Canada, an evangelical organization that seeks to convert Jews to Christianity. He travelled regularly across Canada, spreading the word and developing a list of about 5,000 donors who gave generously to the cause.

His career with the ministry abruptly ended in 2005 when Jews for Jesus fired him for allegedly violating the group’s Workers’ Covenant by secretly dating and then getting married at Toronto City Hall. Mr. Araujo has gone to work for a rival organization, Chosen People Ministries Canada, and he is suing Jews for Jesus in an Ontario court for wrongful dismissal.

The lawsuit has taken a twist with Jews for Jesus countersuing Mr. Araujo, alleging that he used its donor list to solicit money for Chosen People. In court filings, Mr. Araujo acknowledged sending a letter to supporters that in part asked for financial support, but he insisted he did nothing wrong because he approached only the donors that he had cultivated during his 12 years at Jews for Jesus.

The case has raised questions about how many evangelical groups operate and who controls donor lists when a key member switches to another cause.

At issue is “designated fundraising,” a method many religious groups use to finance mission work. Instead of the group raising money centrally to send out missionaries, each missionary must find donors to cover his or her salary and other expenses. These donations go the organization, which issues tax receipts, but the money is designated to the individual missionary. Jews for Jesus and Chosen People operate this way and their missionaries regularly make presentations to churches to raise money for their work.

But who gets the donor list when a missionary goes to another organization? And which donors belong to the missionary and which to the church? Those have become a central questions in Mr. Araujo’s lawsuit and for many other religious groups.

“This is a unique case,” said Rev. John Pellowe, chief executive of the Canadian Council of Christian Charities, which represents 3,100 organizations including Jews for Jesus and Chosen People Ministries. He explained that most churches rely on congregations to support regular church activities, but it’s not uncommon for many to require missionaries to raise some or all of their own funding. These churches “end up sending many more missionaries than they could otherwise, because [the missionaries] all tap into their friends and family,” Rev. Pellowe said.

While disputes between charities over these donors are rare, the rules governing them aren’t clear.

In fact, Jews for Jesus complained to the council about Chosen People having access to Mr. Araujo’s list, and the national body spent months trying to find a resolution. Rev. Pellowe said Chosen People eventually agreed to return the names, but Jews for Jesus is still pursuing Mr. Araujo in court.

Jews for Jesus declined comment and Mr. Araujo was unavailable. His lawyer, Barry Goldman, said the case has taken an unusually long time to resolve. He was also unaware of the council’s mediation.

Mr. Araujo started at Jews for Jesus in 1993 as a student. He became a clergyman in the organization three years later and was hired under contract as a “tenured missionary.” By all accounts, Mr. Araujo was a passionate minister, helping organize major campaigns and raising money to cover his $59,000 annual salary and other expenses. Jews for Jesus and Chosen People are both based in the United States and each operates in about a dozen countries.

His career at Jews for Jesus began to unravel on Nov. 4, 2005. Mr. Araujo was in Argentina on mission duties when his wife, Diana Scott, called the Toronto office looking for a way to contact him. Jews for Jesus alleges in court filings that it had no idea Mr. Araujo was married and leaders confronted him on his return.

Mr Araujo told them the couple had married three months earlier in a civil ceremony and Ms. Scott was a “believer,” according to court documents. Jews for Jesus fired him three weeks later for allegedly violating the organization’s lifestyle policies by, among other things, concealing the marriage, failing to obtain counsel from leaders before courting Ms. Scott and failing to “select Scott as [a] spouse in accordance with the dating guidelines of the Workers’ Covenant.” Court filings show the organization has demanded details of Mr. Araujo’s sex life to further prove he violated the Covenant and “the standards of Biblical morality.”

Mr. Araujo said in court documents that he never signed the Workers’ Covenant because he disagreed with the courtship and marriage rules, calling them “cultish.” He also labelled Jews for Jesus’ conduct “callous.”

Shortly after joining Chosen People in January, 2007, Mr. Araujo sent a letter to supporters to announce his new position and seek their prayers and financial support, according to court filings. In its lawsuit, Jews for Jesus alleged the letter went to people on its donor list and that someone inside the organization sent Mr. Araujo the names. It wants him to identify the person. Mr. Araujo said in court filings the letter went to his personal long-time supporters only, and he has refused to say who sent him the names.

Ben Volman, the Toronto director of Chosen People, declined comment on Mr. Araujos’ lawsuit. But he said evangelical organizations have a tough time raising money, and missionaries “are highly pressured to build donor lists.” Once those lists are given to the organization, he added, “do you think the organization just says when the missionary walks away, ‘Oh well, I guess we’ll just let you take your list with you?’... Organizations have a tendency, naturally, to see donors who’ve been acquired as their property.”