Former FBI agents who worked the notorious 1970s sting operation known as ABSCAM have written FBI Director James Comey to warn that nothing less than the bureau's "reputation" is on the line as the investigation into Hillary Clinton's email practices enters a critical phase.

The agents, in a March 16 letter obtained by Fox News, offered their support for Comey and the agents working the email case. But the letter cautioned the outcome would have long-lasting implications.

"Decisions must be made on facts alone. Much is at stake here -- people's trust in the Bureau for years to come, as well as the Bureau's reputation among our allies, partners, and friends as the greatest law enforcement agency in the world,” wrote John F. Good, president of the Long Island Chapter of the Society of Former Special Agents of the FBI.

Good told Fox News a half-dozen FBI agents who worked the 1978 ABSCAM investigation – which targeted sitting members of Congress -- belong to the chapter. The ABSCAM investigation included more than 30 political figures, with six House members and one U.S. senator ultimately convicted of crimes. The investigation was depicted in the 2013 Golden Globe-winning movie "American Hustle," in which Bradley Cooper played an agent based on Good and others.

Good, 79, told Fox News by phone that the Clinton email case boils down to whether the U.S. is a nation of laws, where all citizens are equal under the law, or there is a different set of rules for the powerful. He said the ABSCAM agents thought it was important to show support for the bureau’s work in the email probe since they know what it feels like to face intense public scrutiny.

Good, though, said the pressure the ABSCAM agents faced 40 years ago pales in comparison to what Comey and the agents are dealing with today regarding the Democratic presidential front-runner and her aides.

On “Fox News Sunday” last weekend, President Obama weighed in on the ongoing email investigation, saying his former secretary of state had not intentionally harmed national security, but had been "careless" with her emails. White House Spokesman Josh Earnest later confirmed the president was not briefed on the investigation by the FBI or Justice Department, and had based his statements on media reports.

Obama, meanwhile, repeatedly vowed there would be no political influence in the case.

Good said that at the outset of ABSCAM, then-FBI Director William Webster had their backs and told them, "The future of the FBI rests on this case."

He said the same holds true today, but added that the retired agents are concerned Comey may not have the same level of support from the Justice Department, where Attorney General Loretta Lynch will make the decision on whether a prosecution is pursued.

"It does not appear that the same relationship between the FBI and DOJ exists today on the case," he told Fox News.

Then-FBI agent Good was a central player in ABSCAM. A native of the Bronx, and son of an FBI agent, he was known for his expertise navigating the tricky business of selecting and developing informants. In 1977, Good had been working on an ongoing inquiry into payoffs to officials in Suffolk County, N.Y., during a sewer project but the pressure from the bureau was to develop bigger and more major cases.

So in 1977, Good selected a crook's crook by working with a colorful swindler from Long Island named Mel Weinberg (the basis for the “American Hustle” character played by Christian Bale) to ferret out widespread government corruption. The undercover operation featured agents posing as phony Arab sheiks toting suitcases full of cash and stolen artwork, all caught on 1,000 hours of videotape.

Now 91 and living in Florida, Weinberg told Fox News that "the country is going to pot. Today's politicians are too smart, the money is greater and they all learned from ABSCAM."