FIRST ON FOX: Several former and current members of the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) are sounding the alarm against President Biden's nomination to lead the agency.

Former ATF Director Michael Sullivan, as well as a current ATF member involved in training and a retired ATF deputy director who wished to remain anonymous out of fear of retaliation, expressed concern that Biden's nominee is too political to lead an unbiased agency.

"I am concerned that somebody who has taken such a strong and hostile position against the Second Amendment, as well as gun owners and some of the most popular firearms in the United States, would be viewed as a political leader for an agency that, I think, has worked extremely hard to build the American public confidence in its handling of interpreting both the Gun Control Act and the various regulations around it," Sullivan told Fox News.

The Senate Judiciary Committee is holding a vote on Chipman's nomination to lead the bureau on Thursday morning. Chipman was an ATF special agent for 25 years and currently serves as senior policy adviser to gun-violence prevention group Giffords.

Giffords Law Center Senior Policy Adviser David Chipman speaks at a House Judiciary Committee hearing on assault weapons on Capitol Hill in Washington. (AP Photo/Andrew Harnik, File)

The current and former ATF agents who spoke to Fox News described Chipman as an "activist" who is not right for the role of ATF director. The ATF has two missions related to gun regulation: enforce gun laws and regulate gun manufacturing, importing and sales. The ATF director, therefore, can impact what the agency interprets as lawful or unlawful.

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"Mr. Chipman has made it clear over the course of his time as a lobbyist with organizations that are anti-gun and one that has a very restrictive view of the Second Amendment ... would suggest a hostility toward both the Second Amendment and the American people’s right to exercise their constitutional rights under the Second Amendment to be firearm owners," Sullivan said.

He added that the "vast majority" of American gun owners legally own their weapons and use them lawfully. 

"Those are the ones who would be adversely impacted by … the ability for the [ATF] director and the director's legal team to influence regulatory and enforcement decisions within the agency," Sullivan said.

During his tenure at the ATF, Chipman "disrupted firearms trafficking operations in Virginia that were supplying illegal guns to New York City," and was named special agent in charge of ATF’s firearms programs, according to his bio on Giffords' website.

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Chipman also received the Attorney General’s Award for Outstanding Contributions to Community Partnerships for Public Safety in 2005 for his efforts to combat local violent crime and served on the Firearms Committee of the International Association of Chiefs of Police.

The current ATF member who spoke on the condition of anonymity described Chipman as a "bully" during his time in Detroit.

Former Bureau of Alcohol, Tobacco, Firearms and Explosives agent and Giffiords Law Center senior policy advisor David Chipman (R) testifies before U.S. House Judiciary Committee. (Photo by Chip Somodevilla/Getty Images)

"His reputation is as an activist more so than anything," he said. "I’ve only known two ATF agents out of hundreds whom I would describe as being anti-gun, and Dave is one of them."

The agent, who is involved in training for the agency, said later on that unlike the Drug Enforcement Agency (DEA), which regulates commodities that are always unlawful, American-owned guns "are more often than not legal."

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"To effectively enforce [gun] laws, you have to be unbiased and apolitical," he said. "You can’t be partisan. Dave has shown himself to be a rabid partisan. He’s shown a propensity who personally attack people who don’t share his ... philosophies. He ... I guess, perceives that he is on some sort of platform of righteousness."

The former ATF deputy director echoed this sentiment, describing Chipman as "not a popular leader" and "very engaged in gun issues ... probably more than he should have been."

"It’s not for ATF to determine pro or anti-gun issues. That’s for Congress and the public and the people they elect. It’s not ATF’s mission. Putting someone in charge of the agency that’s coming in with an agenda that’s politically based for  the organization that’s charged with managing and overseeing that business entity is just not appropriate," he said.

He continued: "Ultimately, I think [Chipman's nomination] is bad for the agency. No more should the ATF be led by someone that’s an NRA lobbyist than they should be led by someone who’s coming from [Giffords] or something like that."

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The former ATF deputy director said he believes the Senate will confirm Chipman to lead the ATF on Thursday but that it will result in overregulation of the gun industry.

"I never thought the ATF should never be in a position to overregulate. That’s Congress’ job," he said. "I think you’re going to see a lot more intent to regulate [if he’s confirmed]."

He added that if Congress is unable to pass gun reform policy, "the administration is then going to turn to ATF and expect them to execute regulatory functions that are probably beyond the scope of ATF’s legal authority potentially," which he said he think Chipman will "be quite willing to do."

Sullivan said that he believes Chipman's intentions are clear: "To restrict the ability of the American public to get access to firearms."

Chipman has expressed skepticism about the feasibility of confiscating assault weapons from their current owners.

In an op-ed he penned in The Roanoke Times last year, Chipman described himself as a "proud gun owner" who has sometimes been "mischaracterized as a gun grabber." Chipman noted that he supports gun safety regulations that would "save lives" but wouldn’t take guns away from law-abiding citizens.

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"I am a proud and responsible gun owner, as are millions of Virginians," Chipman wrote. "I am also permitted to carry a concealed handgun. I am not afraid of lawmakers in Richmond passing laws to make it harder for criminals to get guns. In fact, I’m part of the majority who demand it."

ATF is a law enforcement agency within the Department of Justice that strives to safeguard the public from criminal organizations and activity, including the illegal use and trafficking of firearms.

A number of law enforcement groups, ATF agents have and attorneys general have expressed support for Chipman in letters posted to the Senate Judiciary Committee's website.

Fox News' Brittany De Lea contributed to this report.