“[D]espite Facebook’s ban of gun sales on its platforms, users are nonetheless able to facilitate firearm transactions in private Facebook groups specifically designed to skirt Facebook’s ban on firearm sales,” the 13 senators wrote in the letter to Facebook CEO Mark Zuckerberg.

Facebook first banned the sale of firearms on the platform in 2016, then in 2018 it added proactive measures to identify sellers after pressure from lawmakers.

“We have concerns that those measures fall short,” the lawmakers lead by Sens. Bob Menendez (D-N.J.) and Ed Markey (D-Mass.) wrote in the letter to Facebook.