Philadelphia Mayor Michael Nutter wasn’t joking.

Roughly 50 teens were arrested on the first night under the city’s new curfew for teenagers. Last week, Nutter instituted a weekend curfew of 9 p.m. for teens under 18 in Center City and University City Philadelphia in an effort to control attacks by flash mobs.

In addition to extending the hours of 20 youth centers in the city, Nutter’s plan also involves more police manpower and a push to get business leaders to register their security cameras with the police department.

Arrests started around 9 p.m. on Friday in downtown Philadelphia and South Street, and first-timers are looking at fines of $100-$300. Time will tell if the arrests and fines slow the flash mobs down, but it’s only a matter of time before people start taking justice into their own hands.

[via Fox News]