O'Brien says Archdiocese of Baltimore won't offer birth control coverage
"We have gotten off to the wrong debate — and the wrong discussion," Mikulski said. "Let's get back to how we improve the health care of women."

At least one poll shows that some Catholics may not agree with the leadership of the church on the issue. About 53 percent of Catholic voters support the requirement of birth control coverage by religious groups, according to a poll conducted by Public Policy Polling for Planned Parenthood. Planned Parenthood and the Catholic Church often clash over issues of birth control and abortion.

David Cloutier, associate professor of Mount Saint Mary's University in Emmitsburg, said the church is turning it into a broader issue of church freedoms, rather than just about birth control.

"There was very little in the letter about contraception," he said. "But there was great deal about the way in which religious freedom was being threatened."

Cloutier heard O'Brien's message read during Mass at St. John the Evangelist in Frederick. He said the church seems to feel that cutting off insurance would be the only way to "to follow the conscience of the institution."

The Archdiocese of Baltimore covers about 3,500 people who work for various Catholic schools and nonprofits. The institution has its own health insurance plan.

If it were to decide not to cover employees, those people would have to buy insurance from exchanges, or open markets that are being set up for people who aren't covered by employer insurance.

Salganicoff at the Kaiser Family Foundation said it would be more complicated for people to have to buy for the open market. She said it would also go against the purpose of health care reform to make coverage more accessible.

"The goal is to improve employee-sponsored coverage, not to put push people out of their workplace coverage," she said.

Employers will be required to pay varying fees if they don't offer insurance under health care reform. O'Brien said in his letter that that is something the archdiocese would be willing to do.

If the federal government doesn't agree to the changes, religious groups could file lawsuits in court or try to persuade Congress to change the provision legislatively.

For now, Caine said, the archdiocese will continue to ask its parishioners to call their elected officials to speak out against the birth control rule. The archdiocese is also staying in constant contact with U.S. Conference of Catholic Bishops to fight the issue.

Reuters contributed to this article.