"This safety issue must be addressed promptly, before the expansion of pre-kindergarten brings thousands of additional three and four year-olds into school buildings this fall," the letter says.
"I call on you, Mayor de Blasio, to put our children's safety first and make the 'Audible Alarms Bill' law."
The New York City Parents Union's petition had been signed by 216 supporters as of Wednesday morning.
The group also launched a website, getitdone4kids.org.
The bill, sponsored by Bed-Stuy and Crown Heights Councilman Robert Cornegy, would require all public schools with elementary or special needs students to install alarms on every exit but the front entrance, which is normally watched by a security guard.
Cornegy drafted the bill after a string of incidents in New York in which at least six children walked out of school buildings without staff knowledge, including autistic 14-year-old Avonte Oquendo — who was later found dead — and Symeir Talley-Jasper, a pre-K student who left his Bed-Stuy school and walked home safely.
Supporters have called it an affordable solution. P.S. 59, Symeir's school, installed similar alarms at a cost of $139 per door, according to the Cornegy.
Cornegy said he launched the "audible alarms" idea after talking to the parents of Symeir, and appreciated the support of the parents who created the petition.
“Parents have been the driving force behind the Audible Alarms bill from the first day,” Cornegy said. “So it’s completely appropriate that parents are now organizing to demand this change.”