Updated

A lawyer for two Arizona gun dealers argued Wednesday that the Obama administration overstepped its legal authority in trying to halt the flow of U.S. guns to Mexican drug gangs when it required dealers in border states to report when customers buy multiple high-powered rifles.

Attorney Richard Gardiner told a federal appeals court panel that the directive requires gun dealers to create a records system and the government has no authority to do that.

At issue is a requirement that the Bureau of Alcohol, Tobacco, Firearms and Explosives imposed in 2011 on gun sellers in California, Arizona, New Mexico and Texas. The requirement compels sellers to report to the ATF when anyone buys -- within a five-day period -- two or more semi-automatic weapons capable of accepting a detachable magazine and with a caliber greater than .22.

The bureau says the requirement is needed to help stop the flow of guns to Mexican drug cartels.

Gun issues are in the spotlight these days as the Obama administration works on new policies to tackle gun violence after last month's school shooting in Connecticut. Tracking guns and limiting gun and ammunition purchases are among the ideas suggested so far by advocacy groups, officials and others.

In Wednesday's arguments, Judge Harry T. Edwards asked Gardiner if the model number on a rifle would indicate whether it was covered by the requirement.

"It might," Gardiner replied, but he added that the person doing the record-keeping might not be able to tell.

Gardiner, who is representing J&G Sales, Ltd. and Foothills Firearms, LLC, said that nothing in the law allows for the presumption that the federal licensee would have that knowledge.

Justice Department lawyer Michael Raab said sellers should be able to determine by the manufacturer and model number if a particular rifle is covered by the requirement. He said sellers were told they can call the ATF's firearm's technology branch if they have questions.

"We're not aware of any requests or confusion," he said.

The third judge on the panel, Karen LeCraft Henderson, asked Raab about a measure Congress passes every year banning the ATF from establishing a national firearms registry. Raab noted that the ATF already requires sellers nationwide to report when someone purchases two or more pistols or revolvers within five days. That is not being challenged in this case. The ATF demand letter at issue here, Raab said, is "much narrower."

Last year, U.S. District Judge Rosemary M. Collyer rejected a challenge to the ATF requirement by the two Arizona gun sellers and the firearms industry trade group, the National Shooting Sports Foundation.

The trade group argues that the agency didn't have the legal authority to issue the requirement, and even if it did, its decision to impose it on every retailer in the border states was arbitrary and capricious.