Hundreds of people were seen ignoring social distancing guidelines in Williamsburg on Tuesday night.
The funeral was held for Rabbi Chaim Mertz.
Video shows hundreds of people jammed together in the streets for the service.
In a series of angry tweets, de Blasio said this type of gathering will not be tolerated and the time for warnings has passed.
"We have lost so many these last two months and I understand the instinct to gather to mourn, but large gatherings will only lead to more deaths and more families in mourning," he wrote on Twitter. "We will not allow this."
He said he has instructed the NYPD to make arrests if necessary, however no arrests were reported.
MORE CORONAVIRUS COVID-19 COVERAGE
COVID-19 Help, Information and Resources
UPDATES
[Ads /]
Grieving the lost: Tri-State residents who have died
New York state
New Jersey
Connecticut
Long Island
[Ads /]
RELATED INFORMATION
[Ads /]
Share your coronavirus story with Eyewitness News
Stimulus check scams and other coronavirus hoaxes
Coronavirus prevention: how clean are your hands?
Centers for Disease Control and Prevention on coronavirus
Total count of NYC COVID-19 cases based on patient address