BOSTON -- Stop Handgun Violence unveiled its latest 250-foot billboard next to Lansdowne Street, encouraging Congress to close the so-called gun show loophole.

NewsCenter 5's Sean Kelly reported on Tuesday the new billboard is part of a renewed push to change federal law that critics say allows criminals, even terrorists to buy guns at gun shows without background checks.

Team Investigates New Push To Keep Criminals From Buying Guns

Earlier this year, Team 5 Investigates went undercover to a gun show in Vermont to see how easy it would be to buy a gun illegally. Within minutes, our investigative team encountered a private seller who was well aware of the law, and who told us he was more than willing to break it.

Seller: "I'm not really supposed to sell handguns."

Team 5: "I was just hoping I'd be able to find somebody up here and let money do the talking you know."

Seller: "Well, you know the old Italian saying, make me an offer I can't refuse. You know what I mean? Then we can do something illegal."

Team 5: "I'm willing to do $2500 cash."

Seller: "$2500 cash? That's tempting. I was figuring around the same thing. You got that kind of money?"

Team 5 Investigates told him we'd have to get it. But we never did go back to purchase the gun and no laws were broken.

Now, Team 5 Investigates has learned the ATF is investigating other transactions conducted by that dealer although the ATF would not confirm or deny the ongoing investigation.

"Does it surprise you that we were able to do that so quickly?" asked Kelly. "It does not surprise me. That's why it's important to close the gun show loophole," said U.S. Sen. Jack Reed, D-RI.

Reed is renewing his push to require everyone who sells guns at gun shows to do background checks. Right now, only federally licensed dealers are required to do them. "We have to have one standard for the acquisition of firearms in public places like gun shows," said Reed.

Advocates of Reed's proposal believe it would help cut down on street crime and help keep weapons out of terrorists' hands. "There are some people who are going out deliberately buying weapons without any sort of paperwork through private sales of gun shows and the weapons find themselves on the streets of big cities and are used in gun crimes," said Reed.

But the senator says getting the rest of Congress to go along with his proposal will not be easy, considering the National Rifle Association's resistance. "Their opposition seems to be constant and continuous. Forget the merits of the case, it's just that they're in the business of preventing any sensible gun legislation," said Reed.

The NRA says the legislation now before Congress goes too far and the senators' claims that this bill would only impact gun sales at gun shows are false.