Over 20 laser strikes were conducted on aircraft across the country overnight, prompting an investigation from federal authorities. Despite enacting stricter penalties for those who shine the devices at aircraft, laser strikes are growing in frequency. The lasers have the ability to temporarily blind pilots.

According to USA Today, three laser strikes were reported to the Federal Aviation Administration last night in the New York City area. An additional three strikes were reported at Dallas Love Field. Individual strikes were reported in Los Angeles, Salt Lake City, Detroit, San Juan, and a handful of other cities.

Through the middle of October, 5,352 reported strikes occurred this year. Back in 2010, the FAA received reports of around 3,000 strikes. According to the FAA, none of the strikes overnight led to any pilot injuries.

The cities with the highest number of strikes are Los Angeles, Phoenix, Houston, Las Vegas, and Dallas, with over 100 strikes each. The lasers pose a danger to aircraft because the light spreads across the glass of the cockpit. This can cause temporary blindness to the pilot during takeoff and landing. In the past, affected pilots have needed to seek medical attention.

Since 2011, the FAA has had the authority to fine an individual up to $11,000 in civil fines for aiming a laser at an aircraft. A 2012 law made the act a federal crime, punishable by up to 20 years in prison with a $250,000 fine. From 2012 to 2013, 96 out of 152 investigated cases had actions taken out by the FAA.

Because lasers are difficult to track from the ground, the FBI encourages witnesses to report any laser strikes to their local FBI field office. Some officials have called for the sale of high-powered, long-range lasers to be banned by the FDA.