Arizona's new law cracking down on illegal immigrants could "seriously obstruct, or even undermine" the delivery of health care services in the state because doctors and hospitals fear they may be criminally charged if they provide care to illegal immigrants, a Phoenix doctor says.

In a letter published in the New England Journal of Medicine, Dr. Lucas Restrepo of the Barrow Neurological Institute at St. Joseph's Hospital in Phoenix said the law "threatens one of the oldest traditions of medicine: physicians shall protect patients regardless of nationality or race."

Under the law, which is set to go into force at the end of July, "it can be argued that health care providers who neglect to report illegal immigrants under their care will violate the law and be considered criminals," Restrepo writes. "The bill provides physicians with no guidance as to what constitutes 'reasonable grounds' to suspect that somebody is in the country illegally, leaving the particulars of such scrutiny to anyone's imagination."

Restrepo's letter joins a growing chorus of professionals who see a threat to their work in the controversial Arizona law, which, among other things, allows police to question and detain anyone they believe may be an illegal immigrant, even if they are not suspected of committing another crime. The law would also require anyone in the state suspected of being an illegal immigrant to show some kind of document proving citizenship, like a "green card" permanent residency document or a passport.

Last week, a group of Arizona police chiefs declared their opposition to the law, saying it would increase crime by driving a wedge between police forces and immigrant communities.

The law "will drive a wedge between the community and the police, and will damage the trust that police agencies have worked to establish over many years with members of all their communities," the police chiefs said in a statement.

In a meeting with US Attorney General Eric Holder, the police chiefs were reportedly told that the federal government plans to challenge the Arizona law in court.

In his letter, Dr. Restrepo urged doctors and hospitals "to ponder the extent of their liability under the new law and draft clear institutional policies to defend their patients and employees from potential harassment."

Dr. Restrepo was one of three staff members at the Barrow Neurological Institute who signed a letter to the editor of the Arizona Republic in April declaring that the law could expose doctors to criminal prosecution.

"It is unclear whether health-care professionals like ourselves will infringe on the law if we don't report patients or their families to the police or immigration authorities based on a vague suspicion of illegality," the letter, published one day after the bill became law, stated. "Asking patients to produce a passport violates the trust that we endeavor to earn from them."

Many critics of the Arizona law, including President Obama, have said the law opens the door to the possibility of legalized discrimination against Latinos. Despite the concerns, polls indicate that more Americans support the law than oppose it.