NRA Sources tell NBCNewYork they've downgraded Gillibrand from an A to an F, a move scheduled to be announced later this week.
When Gillibrand was appointed to the Senate last year, she boasted about sleeping with guns under her bed and how her family hunted their own Thanksgiving turkeys.
She was also proud of her perfect letter grade from the NRA, which said she had voted with them on gun related issues 100 percent of the time as an upstate Congresswoman.
But since she joined the Senate, the powerful gun-lobbying group says she has voted against them 100 percent of the time.
NRA spokesman Andrew Arulanandam tells NBCNewYork it is highly unusual for a politician's score to change so much in such a short time. He could not recall a similar instance in recent history.
"Kirsten Gillibrand either lied to her constituents in the 20th district, or she's lying to all New Yorkers today. Either way, the operative word is 'lie,'" he said.
Gillibrand denied she is a flip flopper. "Not at all. I still support the Constitution completely," she said. When NBCNewYork asked the Senator how she feels about the dramatic change in her NRA score, the Senator said "My interest is not in what any one group thinks or feels. My interest is being a voice for New Yorkers."
Gillibrand has reversed positions on some gun legislation that she herself sponsored before becoming a senator. She attributes the change to becoming educated by people like Mayor Bloomberg about the influence of illegal guns on urban crime.
She has since introduced a state of the art anti-gun trafficking bill to crack down on the illegal weapons being used in 90 percent of gun crimes, something she promised she would do after meeting with parents of victims of gun violence immediately after being appointed.
Many New Yorkers, at least here in the city, see a failing grade from the NRA as a positive, though some are disturbed by Gillibrand's complete turnaround on the gun issue.
While the "F" itself may not hurt Gillibrand, the NRA may decide to spend money to try to unseat her.