Two of America's best known mayors, Michael Bloomberg of New York City and Cory Booker of Newark, said this week that it's time for the acrimonious practice of illegal online gun sales to finally end.

Newark, New Jersey Mayor Cory Booker said, "Gun sales without background checks fuel gun trafficking and violent crime in America's cities."

"While police officers in Newark and across the country continue to put their lives on the line, Washington continues to drag its feet," he continued. "Closing this glaring loophole is not about infringing upon gun rights – it’s about enforcing the reasonable gun sale standards that we as a society have agreed upon for the safety of our families, our police officers, and our communities."

“Who has to get murdered before Congress is going to stand up and say enough of this?" New York City Mayor Michael Bloomberg asked, repeating a charge he also made recently to NBC News. "You'd think if a Congresswoman got shot in the head that would have changed Congress' views."

Bloomberg, who recently carried out his own investigation into online gun sales, is part of a group called "Mayors Against Illegal Guns," which has since 2006 called upon Congress to close the private gun sale loophole and require background checks for everybody purchasing a firearm, even online.

Both mayors and their organization say unregulated online gun sales allow drug users, convicted felons and wanted criminals to buy deadly weapons with no questions asked.

Their organization reached out to members of the press after NBC News recently featured a startling report in which their investigators were able to buy weapons of war powerful enough to take down helicopters and airplanes, just by contacting strangers on the Internet.

In Bloomberg's investigation, 25 different gun-selling websites were contacted, and investigators told the sellers up-front that they would not pass a background check. Ultimately, New York police said that 62 percent of the sellers went through with the transactions, even though it's a felony to knowingly sell a firearm to someone who would not pass a background check.

More than 500 mayors are now part of Bloomberg's group, spanning 40 states. The U.S. Department of Justice says that there are over 4,000 websites in the U.S. that offer private gun sales.

Despite the mayors' agitating, the Obama Administration has been reluctant to push forward with reforms to the nation's gun laws, and conservatives almost universally see private gun sales as a constitutionally protected right.

The video below is from NBC News.

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Updated for clarity.