Connecticut Senators Richard Blumenthal and Chris Murphy joined Congresswoman Elizabeth Esty and gun safety advocates in Hartford on Monday to urge firearms dealers to wait until background checks are complete before selling a weapon.

Federal law allows dealers to sell a gun after 72 hours even if a background check is still pending. It's called a "default sale."

"A lot of people believe that licensed gun dealers must complete a background check before they sell a gun," said Senator Blumenthal. "The fact is there is a loophole: gun dealers are permitted to sell after three days if there is no completed background check."

Murphy said the loophole in the Brady Handgun Violence Act put guns in the hands of 15,729 people over the past five years who were not legally eligible to obtain one, including Dylann Roof, the gunman who shot nine church-goers in Emanuel AME Church in Charleston back in June.

"The people of Charleston know that -- had there been a law on the books demanding that a gun sale not be made without a background check -- there would likely be people still alive in South Carolina today," said Murphy.

A growing number of gun sellers, including Wal-Mart, do not allow default sales. But other major retailers, including Cabela's, EZ PAwn, and Bass Pro Shops will sell guns without a background check after three days.

In a letter to those retailers, Senators Blumenthal and Murphy -- along with eleven other senators -- urged them to wait to sell until a background check is complete.

Read below the full text of the letter sent to Cabela's, EZ Pawn, and Bass Pro Shops:

To Cabela’s, EZ Pawn, Bass Pro Shops and the National Shooting and Sports Foundation,
We are writing you with a simple ask: stop selling guns to people who do not first definitively pass a background check. The senseless killing of nine innocent people in Charleston, S.C., on June 17, was made possible because the alleged gunman was able to buy a gun without passing a background check.

A “default to proceed” loophole in the Brady Handgun Violence Act allows, but does not require, gun retailers to proceed with a firearms sale after three days, if an applicant’s background check is still pending. While certain facts remain unknown, the FBI acknowledges that a fully completed background check would have uncovered the alleged perpetrator’s prior arrest on a drug charge and his drug addiction, thereby barring him from purchasing the .45-caliber handgun with which he took nine lives.

The perpetrator’s exploitation of this loophole is not an anomaly. In the last five years, the “default to proceed” loophole has led gun retailers to proceed with 15,729 firearm sales to “prohibited people” – individuals who were deemed ineligible to purchase a firearm once their background checks were completed.[1] Based on FBI data, the Brady Campaign estimates that on average more than ten prohibited people a day are sold guns by gun dealers who do not use their discretion to wait for a final determination from FBI. Responsible gun retailers can act today to address this unacceptable situation. The law allows retailers to decide whether or not to allow gun sales to proceed after the three-day “default period” has elapsed. You have a duty to ensure that your products do not get into the hands of dangerous individuals like the Emanuel AME Church shooter.

In 2008, Walmart, the nation’s largest gun retailer, partnered with Mayors Against Illegal Guns and agreed not to transfer firearms without background checks, even if three days had passed. The short-term inconvenience is minimal. In the vast majority of cases the background check is completed within minutes and the retailer knows whether they may proceed with the sale. After the horror inflicted upon the Emanuel AME Church in Charleston, no responsible gun retailer should transfer a gun without first conducting a complete background check.

We implore you to act now. Join the movement of responsible gun retailers both large and small who will not sell a firearm absent a complete background check.