New York City health officials issued summonses to parents of three children Thursday for failing to have their children vaccinated against measles, a violation of the city’s emergency order mandating immunizations to control a surging outbreak.

The adults face civil penalties of $1,000 if an officer upholds the summons at a hearing. Health officials identified three children who were exposed to the severe respiratory virus but were not yet vaccinated by April 12, in violation of the order. Failing to appear at the hearing or respond to the summons will result in a $2,000 fine but city authorities have said they will not face criminal prosecution. The children are in three separate households.

Public health legal experts said it’s been at least a century since health authorities issued fines in connection with such violations.