A good Marine is being put through the wringer -- with his career now hanging in the balance -- for mistakenly sending a threat warning from an unclassified email account, according to supporters.

The 2012 warning from Jason Brezler, a Marine Corps reservist and New York City firefighter, told his fellow Marines that a senior Afghan police official was a security risk, including allegations that he sexually abused minors on U.S. bases in Afghanistan. One of the Afghan official's assistants and purported victims, days later, opened fire and killed three U.S. Marines.

But Brezler's supporters say his career is now in jeopardy because of political correctness and a genuine fear that revealing the facts of his case will expose the underbelly of U.S. policy in Afghanistan.

"Brezler's immediate chain-of-command here in the U.S. did not recommend punitive action, and the Marine command in Afghanistan called for the relevant document in Brezler's case to be declassified, because there is no information in the document which, if released, would damage national security," Kevin Carroll, whose firm Quinn Emanuel Urquhart & Sullivan is representing Brezler pro bono, told Fox News.

Brezler now faces a board of inquiry as early as next month where he could be forced from the Marine Corps -- what amounts to an "other than honorable" separation -- for sending the warning from a Yahoo, rather than a classified, account even though Brezler admitted the error to his own supervisors.

Last summer, Brezler received an urgent request for information from his fellow Marines in Helmand Province, Afghanistan. They wanted background information about a senior Afghan police official, Sarwar Jan, who was routinely allowed on base as part of the U.S. strategy to train local security forces before the 2014 withdrawal.

Brezler immediately responded with information about Jan's derogatory background, including the allegations of sexual abuse. There is no evidence immediate action was taken, and days later, one of Jan's assistants allegedly opened fire on the Marines.

In September, Rep. Peter King, R-N.Y., wrote to the Defense Department inspector general that Brezler "suspected Jan had committed sex crimes against juveniles at U.S. Department of Defense facilities in Afghanistan. On August 10, 2012 one of Jan's subordinates and sex-crime victims killed three U.S. Marines, including my constituent Lance Corporal Greg Buckley, Jr."

Buckley, along with Staff Sgt. Scott Dickinson and Cpl. Richard Rivera, were all murdered at Forward Operating Base Delhi after the alleged shooter, a teenage boy who worked for Sarwar Jan as an "assistant," opened fire on the men while they worked out at the gym. Another Marine, Staff Sgt. Cody Rhode, was shot five times and survived.

In a July letter to Commandant Gen. Jim Amos, King said Jan was believed to be a security risk, and Brezler was only trying to save lives. It is "unfair for Maj. Brezler's good-faith effort to warn his fellow Marines, of what sadly proved to be mortal danger, to derail his reserve career. The Marines and the (New York City) Fire Department need more good men such as Maj. Brezler, not less," King wrote. The congressman, who also sits on the Homeland Security and Intelligence committees, said the report about Brezler's actions from March 12, 2013 "contains several administrative irregularities."

Among Brezler's supporters are Medal of Honor recipient Dakota Meyer and Bing West, former assistant secretary of Defense, who wrote the Board of Inquiry in September, that "Brezler is an unvarnished leader. His unwavering quality comes through to other Marines and to the people and government officials in other lands. As Marines, we exist not to occupy space in cubicles. We're expeditionary. What counts is what we do in the field."

Another supporter, New York City Fire Commissioner Salvatore J. Cassano, also wrote a letter of support. "I have met thousands of dedicated members, and Jason represents the top tier of our ranks in character, ability, dedication and leadership," he wrote.

Francis Piccoli, a spokesman at the Marine Corps Forces Reserve headquarters in New Orleans, told Fox News: "Due to the impending Board of Inquiry for Maj. Brezler, it is inappropriate for me to address this issue at this time other than stating that pursuant to a NCIS investigation that substantiated the mishandling of classified information, Maj Brezler has been ordered to show cause for retention in the U.S. Marine Corps before a Board of Inquiry."

A critical editorial was published this week by the Marine Corps Times, calling for a serious rethinking of the Brezler case.

It said: "Brezler's treatment sends the message that in the Marine Corps there's no room for honest mistakes. That's a dangerous precedent to set ... In his quest to recenter the Corps and 'hit the reset button on accountability,' Gen. Jim Amos has said that the new law of the land does not mean 'zero defects.' ... Brezler's case is an opportunity for the Corps to act on Amos' intent -- and do the right thing."