A former U.S. ambassador to the Vatican and the president of The Catholic University of America were among 300 signers of a letter who called President Barack Obama's revision to a federal contraceptive mandate "unacceptable."
They said it remains a "grave violation of religious freedom and cannot stand."
On Feb. 10, Obama said religious employers could decline to cover contraceptives if they were morally opposed to them.
However, the health insurers that provide their health plans would be required to offer contraceptives free of charge to women who requested such coverage.
The change came after three weeks of intensive criticism that Department of Health and Human Services' contraception mandate would require most religious institutions to pay for coverage they find morally objectionable, despite a limited religious exemption.
Now questions have been raised over how the revision announced by the president will pertain to the many dioceses and Catholic organizations that are self-insured.
It is unclear whether the new mandate could still force entities morally opposed to contraception to pay for such services.
The letter was signed by former Ambassador Mary Ann Glendon of Harvard and Catholic University's John Garvey, along with professors and other academics, and Catholic and other religious leaders.
They said it was "an insult to the intelligence of Catholics, Protestants, Eastern Orthodox Christians, Jews, Muslims, and other people of faith and conscience to imagine that they will accept an assault on their religious liberty if only it is covered up by a cheap accounting trick."