CHICAGO (CBS) – Transportation Security Administration officers have detected four firearms in March at the Midway International Airport security checkpoint.

According to a TSA press release, officials discovered the guns on March 8, March 12, March 20 and March 22. Three of the four weapons were 9mm pistols, while the other was a .38 caliber firearm. Three of the four weapons were also loaded.

People found with firearms at security checkpoints are usually referred to local law enforcement and subject to whatever penalties they enforce. TSA gives civil fines from $1,500 to $7,000 for bringing a firearm to a checkpoint, according to its press release.

The number of guns found at checkpoints continues to rise nationwide. TSA found more than 2,600 firearms in 2015 and almost 3,400 in 2016. Officers have found six guns in carry-on luggage at Midway in 2017.