Senator Edward Markey has written an open letter to Facebook and Instagram asking them to ban the sale of guns and ammunition from the two sites.
The Senator has asked for an explanation as to why he was able to find weapons being advertised on both social media platforms. This comes after reports Dallas shooter Micah Johnson bought a used gun via Facebook.
"I remain deeply concerned that gun sales on Facebook and Instagram - or sales posted online but negotiated and concluded offline - may circumvent or violate state and federal laws, resulting in numerous unlawful sales of handguns, assault weapons and other firearms," wrote Senator Markey.
Facebook and Instagram banned the sale of weapons by individual users in January, although companies which sell guns are still allowed to advertise.
The two social networks had already banned the sale of guns without identity checks.