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As her elderly mother was dying, Barbara Johnson lay next to her on the hospital bed, reciting the "Hail Mary." Loetta Johnson, 85, had been a devout Catholic, raising her four children in the church and sending them to Catholic schools.

At her mother's funeral mass at the St. John Neumann Catholic Church in Gaithersburg, Md., a grieving Barbara Johnson was the first in line to receive communion.

What happened next stunned her. The priest refused Johnson, who is gay, the sacramental bread and wine.

"He covered the bowl with the Eucharist with his hand and looked at me, and said I cannot give you communion because you live with a woman and that is a sin in the eyes of the church," Johnson told ABC News affiliate WJLA.

Her older brother, Larry Johnson, couldn't believe what he had seen.

"I walked to the side of the church to console her, because she was clearly distraught," Johnson told ABC News.

Larry Johnson said his sister, who has been in a committed gay relationship for 19 years, composed herself enough to give her mother's eulogy, but then he was shocked at what happened next. The priest left the altar, Johnson said, and didn't return until his sister was nearly finished speaking.

Family members added that the priest failed to come to the grave site, and the burial was attended by a substitute priest found by the funeral director.

Larry Johnson and his sister were outraged at what occurred on "what would already have been the worst day of my life," he said.

They want the priest, the Rev. Marcel Guarnizo, removed from dealings with parishioners. They also believe he owes them an apology.

"This isn't about gay rights and it isn't about Catholic bashing, it is simply about the conduct of a reprehensible priest," said Johnson.

But the head of DignityUSA, a group that focuses on gay and lesbian rights and the Catholic Church, sees the incident as part of a wider problem.

"The reality is, in some ways, it is very emblematic of the hierarchy's approach to gay people, transgender people," said Marianne Duddy-Burke. "There are little messages of rejection that happen all the time."

Guarnizo did not return an email asking for a comment about the incident.

The Archdiocese of Washington had no public comment about the priest's behavior, but issued a statement that indicated Guarnizo should have taken up the matter of whether Johnson could receive communion in private.

"When questions arise about whether or not an individual should present themselves for communion," the statement said, "it is not the policy of the Archdiocese to Washington to publicly reprimand the person."

The archdiocese said it is looking into the incident and that it would handle it as a personnel issue.

Duddy-Burke of DignityUSA believes the response misses the point.

"I would hope that it provides a wake-up call to church leaders to make them see where the extremes of their policy are leading," she said. "My concern is they will just see this as an isolated incident and fail to see the context."

Both Larry and Barbara Johnson have received letters from the archdiocese of Washington apologizing "that what should have been a celebration of your mother's life … was overshadowed by a lack of pastoral sensitivity."

Larry Johnson appreciated the letters and the sentiment behind them.

But in his letter to the archdiocese, Johnson noted that the Church's teachings in relation to personal behavior are complex issues. And he wondered if the priest has any right to determine who is able to receive communion "without any discussion, insight or spiritual awareness" of the person presenting themselves before him.