Gun industry representatives said they would file lawsuits Wednesday challenging new gun-control measures by the Obama administration, an effort the nation's top lawyer vowed to "vigorously oppose."

The Justice Department, facing growing questions over Operation Fast and Furious, a controversial sting targeting Mexican drug cartels and American gunrunners, announced last month that it would begin requiring firearms dealers along the nation’s Southwest border to report multiple sales of certain semi-automatic rifles. The department said such rifles are "highly sought after by dangerous drug trafficking organizations," and the new measures would help "detect and disrupt" weapons trafficking networks.

On Wednesday, the National Rifle Association and the National Shooting Sports Foundation, a trade association, were planning to file separate lawsuits challenging the government’s authority to impose the new requirements. The groups are seeking immediate court orders blocking the Bureau of Alcohol, Tobacco, Firearms and Explosives from implementing the new reporting requirements.

"[We] are committed to cooperating with ATF and other law enforcement agencies ... to investigate and enforce violations of firearms laws," according to a copy of the industry group’s lawsuit not yet filed in court. "However, Congress has conferred only limited authority on ATF to require federally-licensed firearms dealers to submit information regarding firearms sales. In this case, ATF's demand exceeds its authority and is prohibited under federal law."

But, Attorney General Eric Holder said Wednesday the "action we have taken is consistent with the law."

"The measures that we are proposing are appropriate ones to stop the flow of guns from the United States into Mexico," he told reporters in Washington.

When the measures were first announced, a top Justice Department official said they were "tailored to focus only" on multiple sales of semi-automatic rifles with calibers greater than .22 and the ability to accept a detachable magazine. In particular, federal authorities in Arizona, California, New Mexico, and Texas should be notified when multiple purchases are made within a five-day period. Keans’ concern, though, is that the agency will continue to expand the requirements and expose more legitimate buyers to government notification.

The Shooting Sports Foundation’s suit also claims the new requirements will make it "more difficult" for the 8,500 gun dealers affected to assist law enforcement.

Illegal firearms traffickers will simply alter their schemes to avoid and evade the reporting requirement, making it more difficult for retailers to identify and report suspicious activity, Kearns said in a statement.

The NRA's lawsuit, expected to be filed Wednesday afternoon in Washington on behalf of two Arizona gun dealers, said the dealers will incur "economic loss as a result of having to devote employee time to preparing the reports" and will experience "loss of business from both in-state and out-of-state potential purchasers ... who would have bought [certain] rifles but have been dissuaded from doing so because they wish to protect their privacy rights."

Meanwhile on Wednesday, Holder reiterated his promise to take "appropriate action" if the Justice Department's internal watchdog finds wrongdoing on the part of officials who participated in Operation Fast and Furious.

The operation's plan was to follow American purchases suspected of buying guns bound for to Mexican cartels in hopes they would lead investigators to the heads of the enterprises. But hundreds of high-powered rifles and other guns ended up in Mexico, and self-described whistleblowers now accuse ATF of letting the guns "walk" to Mexico even after safety concerns were raised. Weapons linked to the program were used in a December attack along the Southwest Border that killed U.S. Border Patrol Agent Brian Terry.

At least three men have now been charged in connection with the murder, but only one is in U.S. custody.

Holder said letting guns "walk" is "an inappropriate technique" no longer employed by his department, as outlined in an internal memo made public in March. He said the matter is "something that we take very seriously," and that is why he ordered his department's inspector general to investigate.

"We will look at the results of that investigation, and to the extent that people have committed mistakes, we will assess those mistakes and appropriate action will be taken," he said. "The charges that have been raised are of deep concern to me, ones that I [take] very, very seriously. ... To the extent we find that mistakes occurred, people will be held accountable."

But some Republicans on Capitol Hill, who are leading their own congressional investigation into Operation Fast and Furious, have said they believe people need to be held accountable now.

While Holder didn't know about the operation as it was being carried out, he "should have known," Rep. Darrell Issa, R-Calif., chairman of the House Oversight Committee, told Fox News in June.

"I believe it was his obligation to know, " he said. "The fact that there was a 'Don't Ask, Don't Tell' policy in Eric Holder's office is to say really he wasn't doing his job. ... Nobody is being held accountable -- the U.S. Attorney's Office [in Arizona] or [at] Justice. That has to change."