The California Medical Association is seeking to join the ACLU of Northern California in its lawsuit against a Catholic hospital system over one of its facilities' refusal on religious grounds to allow a doctor to perform a tubal ligation after a planned Cesarean section.

The Medical Association says it's illegal for Dignity Health's hospital administrators to intervene in the decision to tie a woman's tubes after a C-section.

"It's the physician, with his or her patient, who should make that decision," says Dr. Ruth Haskins, the Medical Association's president-elect. "It should not be administrators, who are laypeople, making medical decisions that have such a consequence."

The Medical Association is involved in at least half a dozen lawsuits at any one time, but this is the first time it has moved to take legal action against a hospital system over its religious rules, says Association legal director Long Do.

The suit stems from a case at Mercy Medical Center in Redding, one of Dignity Health's 29 hospitals across the state. Mercy Medical says its refusal to perform the procedure was based on the Ethical and Religious Directives for Catholic Health Care Services, written by the U.S. Conference of Catholic Bishops. The Directives - followed by all of California's 35 Catholic hospitals - prohibit birth control, abortion and, in most cases, sterilization.

The Medical Association, which represents more than 41,000 doctors, is asking the San Francisco judge hearing the case to issue an injunction that would prevent Dignity Health hospitals from using the Directives to block tubal ligations after C-sections.

The American College of Obstetricians and Gynecologists says tying a woman's tubes immediately after a C-section is the "ideal time" to perform the procedure, "because of technical ease and convenience for the woman and physician."

Dignity Health says it's disappointed the Medical Association is seeking to join the ACLU's suit. It says its hospitals inform their physicians about the Directives, and are open about which services they do and don't offer.

Lori Dangberg, vice president of the Alliance of Catholic Health Care, which lobbies on behalf of the state's Catholic hospitals, calls the Medical Association's decision to join the suit "surprising and disconcerting," adding, "it really does put CMA squarely in support of ACLU's long-standing attack on Catholic health care's free exercise of religion."

The Medical Association is not trying to block hospitals' use of the Directives, but it is trying to prevent them from making medical decisions based on non-medical guidelines, according to legal director Do.

A court hearing on the Medical Association's motion to intervene is scheduled for May 25 in San Francisco.