Ultra-Orthodox rabbis in New York City say if a proposed law requiring parental consent for a circumcision ritual linked to two infant deaths is enacted they will defy it.

During the ritual, called metzitzah b'peh, a mohel removes the foreskin and uses his mouth to stop the bleeding. At least 11 New York infants are thought to have contracted herpes from the practice, two of whom died and two of whom have irreversible brain damage, according to the New York City Department of Health and Mental Hygiene.

But rabbis insist 5,000-year-old ritual is safe, and say they refuse to tell parents there are any health risks.

"This is the government forcing a rabbi practicing a religious ritual to tell his congregants it could hurt their child," said Rabbi David Niederman, executive director of the United Jewish Organization of Williamsburg. "If, God forbid, there was a danger, we would be the first to stop the practice."

Niederman said the research linking metzitzah b'peh to infant deaths is "full of holes," adding that the ritual is performed safely "tens of thousands of times a year" worldwide, and that babies who aren't circumcised can also acquire herpes shortly after birth.

"We are convinced that the data is flawed and there's no risk whatsoever," he said, adding that "safeguarding the life of an infant" is one of the Torah's most important principles.

Most modern mohels remove the blood with a sterile pipette. But about two-thirds of boys born in New York City's Hasidic communities, who are ultra-Orthodox, are circumcised in the oral suction manner, Rabbi David Zwiebel, executive vice president of the Orthodox Jewish organization Agudath Israel of America, told ABC News in March.

The Department of Health argues parents should be informed of the risks before making a decision. Since 2004, it has received "multiple complaints from parents who were not aware that direct oral suction was going to be performed as part of their sons' circumcisions," according to a public notice.

The law would require mohels to explain the oral suction procedure and its risks, including the possible transmission of herpes simplex virus, and have parents sign a waiver.

Niederman said the government should "do what they feel is right" and advise against the ritual if they think there's a risk.

"But don't put it on the mohel," he said. "Don't force parents to sign something that is against their religious beliefs."

The city's Health Department is scheduled to vote on the proposed law Sept. 13. But Niederman worries a vote to enact the law would force rabbis, who are "among the most law-abiding citizens," to put their religious beliefs first.

"When it comes to the law, we are all there - it's our obligation, according to our religion. But not when the law goes against our religion," he said.