Gun store owners in southwestern border states argued in federal court Tuesday that the Obama administration cannot require them to report when customers buy multiple high-powered rifles.

The Justice Department responded to a lawsuit seeking to block the two-month-old requirement by asking a judge to uphold its legality, arguing the measure could help stop the flow of guns to Mexican drug cartels. It requires sellers in California, Arizona, New Mexico and Texas to give the Bureau of Alcohol, Tobacco, Firearms and Explosives information about purchasers who buy two or more semi-automatic rifles greater than .22 caliber within five days.

Justice Department attorney Daniel Reiss said having a database of multiple purchasers gives ATF agents the power to trace gun sales within minutes, rather than a multi-day effort to trace the weapons back through the manufacturer, to the seller and eventually the buyer. He said two investigations have already been opened in the short time that the new reporting has been required.