3:32 PM PT -- Saquon Barkley is firing back at Tiki Barber ... accusing the NYG legend of hating on him even years before he opted to leave for the rival Eagles.

"you been a hater since I got to New York," Barkley said in a message to Barber on X. "… and all the 'Dead to me' talk don’t smile in my face when you see me."

Barkley added, "lol yup you’re the prime example of loyalty to a team.. I got the deal I wanted, secured more gm which wasn’t given to me before… so if fans are gonna hate me for that so be it! But I never turned my back on my teammates and always had theirs."

Tiki Barber is furious with Saquon Barkley for leaving the New York Giants in favor of the rival Philadelphia Eagles ... saying straight up Monday, "You're dead to me!!"

The NYG legend unleashed the harsh words on WFAN's "Evan and Tiki" just minutes after it was reported that Barkley will ink a three-year deal with Philly worth around $37 million when the new NFL year kicks off later this week.

"He's dead to us now," Barber said of Barkley. "You're dead to us, Saquon."

Tiki was hardly the only Big Blue supporter livid with the move -- numerous fans sounded off all afternoon on X as well.

Even Barber's cohost on the show, Shaun Morash, threw some shade Barkley's way too.

"By the way, Philly," he said, "enjoy the nine games he'll play next year. Enjoy, Philly. Enjoy."

Barber -- who played his whole 10-year NFL career with the Giants -- wasn't just mad at Barkley over the situation, though. He also admitted that the Giants mishandled the matter -- particularly by not franchise-tagging him this year.

Barkley was on Barber's mind even before Monday's news ... as just days ago he warned the 27-year-old tailback not to sign with the Eagles ... claiming it would be an insult to the Giants' legacy.

"Go to Baltimore!" he said. "Go to Houston! Go to L.A. Chargers! Do not go to the Philadelphia Eagles because if you do, that appreciation and respect and reverence that we all have for you, Saquon, will be lost. It will be gone"

"You’re going to turn into one of those people that we hate, and we don’t want that. We don’t. We’ll respect you, but we’ll hate you, and that’s not a good thing."

Sure doesn't seem like Tiki was lying.