Background checks save lives. They are the foundation of any effective effort to reduce gun violence and are associated with lower rates of gun homicides, suicides and gun trafficking in states that require them for all handgun sales.

But current federal law only requires licensed gun dealers to conduct background checks on gun sales. That means criminals, domestic abusers, and people involuntarily committed due to mental health can avoid the very background checks designed to block them from getting guns by simply buying them from unlicensed sellers. In fact, a 2015 survey found that nearly a quarter (22%) of Americans who had acquired their most recent gun in the two years prior reported doing so without a background check. Since the introduction of the federal background check system twenty-five years ago, the Internet has emerged as a massive, unregulated marketplace, where hundreds of thousands of online ads are posted each year by unlicensed sellers on sites such as Armslist.com who often do not have to perform background checks.

Too many people have died and too many lives have been changed forever as a result of this dangerous loophole in our gun laws. In 2012, Zina Daniel obtained a restraining order against her estranged husband, who had a history of domestic abuse. The restraining order prohibited him from buying a gun under federal law, but several days later he met a private seller on Armslist.com and purchased a gun without a background check. The following day, Zina’s estranged husband went to the spa where Zina worked in Brookfield, WI, and killed her and two other women. He wounded four others before killing himself.

Updating the federal law to require background checks on all gun sales is a common-sense way to keep guns away from people who are legally prohibited from possessing them. Since 1994, background checks have blocked over 3.5 million gun sales to felons, domestic abusers, and other people who aren’t allowed to have guns under existing law.

Poll after poll demonstrates the public’s overwhelming support for requiring background checks on all gun sales, including from majorities of gun owners and Republicans. It’s time for Congress to take action to keep guns out of the wrong hands–by updating the law to require background checks for all gun sales.