ST. LOUIS — At least 1,500 people attended Christmas Eve Mass presided by an excommunicated Roman Catholic priest, despite warnings from the archbishop that participating would be a mortal sin.

The Rev. Marek Bozek left his previous parish without his bishop's permission and was hired by St. Stanislaus Kostka Church earlier this month. As a result, Bozek and the six-member lay board were excommunicated last week by Archbishop Raymond Burke for committing an act of schism.

Burke said it would be a mortal sin for anyone to participate in a Mass celebrated by a priest who was excommunicated — the Catholic Church's most severe penalty. Burke, who couldn't stop the Mass, said it would be "valid" but "illicit."

Despite the warning, Catholics and non-Catholics from as far as Oregon and Washington, D.C., filled the church. An overflow crowd viewed the Mass by closed circuit TV in an adjoining parish center.

"I'm not worried about mortal sin," said worshipper Matt Morrison, 50. "I'll take a stand for what I believe is right."

Many wore large red buttons reading "Save St. Stanislaus," and said they wanted to offer solidarity to a parish they believe has been wronged.

When Bozek entered from the rear of the church, the congregation rose and greeted him with thunderous applause.

"It was magic," said JoAnne La Sala of St. Louis, a self-described lapsed Catholic. "You could feel the spirit of the people."

The penalty was the latest wrinkle in a long dispute over control of the parish's $9.5 million in assets.

The parish's property and finances have been managed by a lay board of directors for more than a century. Burke has sought to make the parish conform to the same legal structure as other parishes in the diocese. As a result, he removed both the parish's priests in 2004.

Bozek, a Pole who arrived in the U.S. five years ago, said he agonized about leaving his previous parish but wanted to help a church that had been deprived of the sacraments for 17 months.

To be Polish is to be Catholic, he said, and to be Catholic is to receive the sacraments.

"I will give them the sacrament of reconciliation, the Eucharist. I will visit the sick and bury the dead," he said. "I will laugh with those who are laughing and cry with those who are crying."

Bozek said he doesn't believe that receiving sacraments at St. Stanislaus, especially Holy Communion, puts a Catholic at risk of mortal sin, in which the soul could suffer eternal damnation.

The Rev. Charles Bouchard, moral theology professor and president of Aquinas Institute of Theology in St. Louis, said Burke was following canon law "to the letter" in excommunicating Bozek and the board.

But some argue that St. Stanislaus' more than century-old governing structure holds the same authority as church law and the bishop lacked merit for imposing excommunication, he said.

"Whether the parties should have reached this impasse in the first place," Bouchard said, "is another matter."