Lawmakers are firing back at a proposal by the Obama administration to ban one of the most common bullets used with the popular AR-15 rifle, with more than 100 members of Congress signing a letter opposing the move on ammo.

Word of the  proposal by the Bureau of Alcohol, Tobacco, Firearms and Explosives to ban .223 M855 “green tip” ammunition came out on Thursday and prompted an immediate backlash from sportsmen. House members from both parties and some law enforcement officials were not far behind.

“[The ban] will interfere with Second Amendment rights by disrupting the market for ammunition that law abiding Americans use for sporting and other legitimate purposes,” reads the letter signed by lawmakers and addressed to ATF director Todd Jones.

“[The ban] will interfere with Second Amendment rights by disrupting the market for ammunition that law abiding Americans use for sporting and other legitimate purposes.”

— Letter from lawmakers to ATF

The bullets, which can pierce bulletproof vests used by law enforcement, had previously been approved by the ATF in 1986. The agency now says that because handguns have now been designed that can also fire the bullets, police officers are now more likely to encounter them and so they should be banned.

However, the congressional letter notes that the ATF provides no evidence of the bullet’s danger to law enforcement.

“ATF has not even alleged – much less offered evidence – that even one such round has ever been fired from a handgun at a police officer,” the letter reads.

Many police organizations are also not in favor of the ban.

“The notion that all of a sudden a new pistol requires banning what had long been perfectly legal ammunition doesn’t seem to make a lot of sense to many officers,” William Johnson, executive director of the National Association of Police Organizations, told FoxNews.com

NAPO represents over 1,000 police units and associations and 241,000 law enforcement officers around the country.

Johnson added that the bullets currently banned under the law deserve to stay banned.

“Some bullets… such as ones coated with Teflon, really are specifically designed to defeat bullet proof vests, and we think they should remain illegal,” he said.

But some law enforcement experts support the ban.

“I am definitely for the banning of these rounds… officers worry about them all the time,” former NYPD detective Harry Houck told FoxNews.com, though he added that a ban might not actually keep criminals from getting the ammunition.

Gun control groups support the ban.

"We understand why law enforcement has always been concerned about the threat of armor-piercing bullets," Dan Gross, president of the Brady Campaign to Prevent Gun Violence, told FoxNews.com.

Lawmakers warn that the regulation – especially as it follows on the heels of attempts to restrict lead bullets -- will “result in drastically reduced options for lawful ammunition users.” Already, the ammunition has been cleared from many store shelves by gun owners looking to stock up in anticipation of the ban. The proposed regulation would not prohibit owning the bullets, but it would stop anyone from manufacturing or importing them.

Gun-rights groups also worry that the ban – if allowed to stand – won’t stop with this type of bullet.

“Almost any hunting rifle bullet will go through body armor, so you could prohibit almost any rifle bullet with this. This is the administration redefining the law on its own,” Alan Gottlieb, of the Second Amendment Foundation, told FoxNews.com.

The lawmakers also dispute the ATF’s legal authority to ban the bullets, saying that the proposed ban “does not comport with the letter or spirit of the law.”

The law, which was passed in 1986, gives the agency authority to ban bullets that are “constructed entirely (excluding the presence of traces of other substances) from one or a combination of tungsten alloys, steel, iron, brass, bronze, beryllium copper or depleted uranium.”

However, the congressmen say that the core of these bullets “contains a substantial amount of lead, raising questions about its classification as ‘armor piercing’ in the first place.”

The congressmen also allege that the ATF violated government transparency requirements.

“The Administrative Procedures Act… requires that ‘general notice of proposed rulemaking shall be published in the Federal Register…’ To date, [the proposed ban] has not been published in the Federal Register.”

The ATF has announced that it is currently taking public comments on the regulation until March 16, when it will prepare to issue a final regulation. Comments can be sent to APAComments@atf.gov.

An ATF spokesman emphasized that no final decision has been made yet.

“No final determinations have been made and we won’t make any determinations until we’ve reviewed the comments submitted by industry, law enforcement and the public at large,” ATF spokesman Corey Ray told FoxNews.com.

“The framework is… intended to protect law enforcement while respecting the interests of sportsmen and the industry,” he also noted.

The author, Maxim Lott, can be reached on Facebook or at maxim.lott@foxnews.com