In November last year, a newborn boy in Brooklyn was brought to his pediatrician’s office because he was being unusually fussy after feedings. The doctor discovered a cluster of lesions on the boy’s penis, then learned that during the boy’s recent circumcision ceremony, the circumciser who performed it had used his mouth to suck blood away from the incision.

Like three other babies last year, the boy had a potentially fatal herpes infection following an ancient Jewish ritual known as metzitzah b’peh, or oral suction. The administration of Mayor Michael R. Bloomberg had tried to regulate the practice, over the fierce objections of ultra-Orthodox rabbis, by requiring that the circumcisers have parents sign a consent form that acknowledged their awareness of the procedure’s risks.

More than two years after the regulation was passed, however, the consent forms appear to be rarely used. Meanwhile, the number of herpes infections suspected to have been caused by the practice in New York City jumped last year.

The situation now presents a conundrum for Mayor Bill de Blasio. City health officials have advised that the ritual should never be performed, but the growing ultra-Orthodox Jewish community that cherishes it represents a crucial political constituency for Mr. de Blasio. So he pledged during his campaign to rescind the consent requirement on “Day 1” of his administration and find a solution that would be more acceptable to Orthodox leaders, while still protecting children’s health.