M855 "Green Tip" ammunition.

(CNSNews.com) -- The government watchdog group, Judicial Watch, is suing the Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF) to release all communication records about a proposal to reclassify certain ammunition for the AR-15 rifle as "armor piercing." The Obama administration, through the Department of Justice, had sought the reclassification in early 2015, a plan that more than 200 members of Congress opposed.

The ATF proposal in February 2015 called for no longer exempting 5.56mm SS109 and M855 ("green tip") ammo from the definition of "armor piercing" ammunition as detailed in the ATF 2014 Regulation Guide, said Judicial Watch in a press release.

The watchdog group is seeking all records, including emails, about that ATF plan and filed its lawsuit in the U.S. District Court for the District of Columbia last week because the ATF failed to respond to a March 2015 Freedom of Information Act request about the issue.

AR-15 hunting rifles. (gunsamerica.com)

“This is yet another example of how Obama’s wanton use of the ‘pen and the phone’ attempted to undermine the constitutional rights of all Americans, as opposed to upholding the rule of law,” said Judicial Watch President Tom Fitton. “The Obama ATF simply ignored our request on their ammo ban. Let’s hope the Trump administration finally brings transparency to this out-of-control agency.”

When the Obama administration first pushed for the change, more than 200 members of Congress wrote to then-ATF Director Todd Jones, an Obama appointee. Congress expressed its "serious concern" that the proposal might violate the 2nd Amendment by resricting ammo that had been primarily used for "sporting purposes," reported Judicial Watch.

The letter states that the ATF's move "does not comport with the letter or spirit of the law and will interfere with Second Amendment rights by disrupting the market for ammunition that law- abiding Americans use for sporting and other legitimate purposes.”

The M855 bullets are among the "most commonly used in the most popular rifle in America, the AR-15," reads the letter. "Millions upon millions of of M855 rounds have been sold and used in the U.S., yet 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 idea that Congress intended ... to ban one of the preeminent rifle cartridges in use by Americans for legitimate purposes is preposterous."

"ATF should refocus its efforts on serious threats to law enforcement officers from specially designed armor-piercing projectiles that are intended for use in the sort of handguns commonly carried and concealed by criminals," said the members of Congress in their letter. "Under no circumstances should ATF adopt a standard that will ban ammunition that is overwhelmingly used by law-abiding Americans for legitimate purposes."