The Rev. Fred Daley, 59, and a Roman Catholic priest, was scheduled to be on an AIDS mission to Africa last Sunday.
He had undergone months of training and was preparing to spend more than a year in Lesotho, where one-third of the population suffers from AIDS.
"The airline tickets had been sent," Daley said to ABC News. "There was no condition to that."
It turns out there was a condition, and now Daley won't be going anywhere.
On July 18, Daley was suddenly withdrawn from his mission to Lesotho by its organizers, Catholic Relief Services.
He says the reason: He is gay.
"This whole situation is surrounding homophobia," Daley said to ABC News.
Daley has publicly acknowledged his homosexuality since 2004, but he maintains his vow of celibacy.
Daley has also been an outspoken advocate for homosexual rights, appearing on ABC's "Nightline" with Cynthia McFadden in November 2005.
Michael Wiest, CRS chief executive officer, and Dave Piriano, a CRS vice president, said that it was not Daley's sexuality that had prompted their organization to take him off the mission.
They said that what had concerned them was that Daley was a public advocate of gay rights.
Wiest and Piriano say they were worried about the reaction from their camp in Africa.
"Lesotho [located deep in the southern tip of Africa] is a country of 1 million poor African peasants," Piriano said. "There are different societal norms there."
"Had we known earlier, we could have avoided so much controversy," Wiest said. "It is not that he is a gay celibate priest, but that he is a well-known activist throughout the United States. … We became concerned about his celebrity in the American dialogue distracting from the mission."
"It seems to me very clear that they are coming up with a way to cover homophobia and fear of homophobia," Daley said. The decision reminds him of racist hiring processes and the military's "don't ask, don't tell" policy, he said.
"There is no doubt that this seems like 'don't ask, don't tell,'" Daley said. "If I was a closeted gay priest, there would be no problem. But because I am struggling for the rights of all gay and lesbian people fighting against homophobia in our whole culture -- I am seen as a problem."
CRS officials, however, adamantly denied that they had a de facto "don't ask, don't tell" policy in place.
"It is not 'don't ask, don't tell,'" Piriano said. "He could have told. He could have worn a button!"
Wiest said that CRS was mostly concerned about the prospect of homophobia in Africa.
"There is a certain taboo about homosexuality in this country. Multiply that by 10 [in Lesotho]," Wiest said.
Daley, however, says that CRS workers in Lesotho had accepted his sexuality and knew about his role as an advocate.
"The archbishop of Lesotho welcomed me," Daley said. "I received information from staff in Lesotho that my invitation there has been re-emphasized among the people, but even though the archbishop had no problem, the CRS officials did have a problem."
Daley had been assigned to this particular African community by CRS and says he wonders why he was not simply assigned to another community if there really was an issue with his homosexuality in Lesotho.
Daley sat down with CRS officials Monday at their headquarters in Maryland.
The relief service officials said they wanted to clarify what was, in their words, "a misunderstanding." Daley used the time to confront Wiest and Piriano.