U.S. gunmakers filed suit Wednesday to block requirements that weapons dealers along the border with Mexico report multiple sales of semiautomatic rifles, escalating a fight with the Obama administration.

The Bureau of Alcohol, Tobacco, Firearms and Explosives last month ordered more than 8,000 gun dealers in Texas, Arizona, New Mexico and California to report such sales to try to stem the “iron river” of firearms flowing to violent Mexican drug cartels.

Starting Aug. 14, dealers must report sales of two or more guns to the same person at one time or over any five business days for semiautomatic rifles greater than .22 caliber and with the ability to accept a detachable magazine.

Two Arizona dealers backed by the National Rifle Association filed a lawsuit in Washington, as did the National Shooting Sports Foundation.

They argued that ATF was authorized by Congress to require reporting such information only for handguns, not for semiautomatic rifles. They also said it would unfairly burden gun sellers and strain law enforcement.

The dealers and groups asked the courts to block the ATF from imposing the requirements. Failure to comply can result in losing their licenses to sell firearms.

About 8,500 gun dealers would be subject to the reporting requirement. Some 36,000 reports of multiple handgun sales were made from the four border states in fiscal 2010, according to ATF. Pledging to “vigorously oppose” the suit, Attorney General Eric H. Holder Jr. said the regulations were legal and necessary to halt guns going to the drug cartels.