Megyn Kelly got approval from higher-ups at NBC before launching her hair-raising attack on Jane Fonda, Page Six has learned — but we’re told that prominent members of the organization were then stunned by how far the broadside went.

Peacock Network insiders fear that the take-down — in which Kelly dredged up Fonda’s “Hanoi Jane” episode to argue that the actress was in no position to “say what’s offensive” — will make it even harder for Kelly to book celebrity guests on her show in case they suffer the same fate.

On Monday’s episode of NBC’s “Megyn Kelly Today,” the host announced that she had stayed silent after Fonda had publicly criticized her for asking the “Grace and Frankie” star about her plastic surgery during a September interview.

But after Fonda brought it up again recently, Kelly had decided that “it’s time to address [Fonda’s] ‘poor me’ routine.”

The morning host said that Fonda had happily discussed the topic in other interviews, then launched into a diatribe about Fonda’s controversial opposition to the Vietnam War. (As Joy Behar said on ABC’s “The View”: “To drag the Vietnam War into a plastic-surgery conversation is a real stretch, Megyn. OK?”).

Sources say the public flogging shocked Kelly’s fellow NBC News staffers.

“The problem is that nobody at NBC is controlling Megyn. They paid her more than $20 million to host the 9 a.m. show, and she’s been given too much power. But the fact remains: You can’t say those things, or be so aggressive, on morning TV,” said an insider. “Plus, Megyn was already having trouble booking celebrities — so how is she ever going to book other stars if they disagree and she goes on air later and trashes them?”

In addition to the Fonda face-off, Debra Messing said publicly that she regretted going on the show to promote the “Will & Grace” reboot, and some publicists have privately said they are disinclined to book talent on her show.

A rep for the show did not comment.