Hayden Panettiere: Neutrogena Flooded With Hate Mail After Her Death

Hayden Panettiere's shocking death has put a target on Neutrogena's back ... and it's getting ugly for the skincare brand that cut ties with her years ago, allegedly over her postpartum comments.

Here's the deal ... Hayden was the face of Neutrogena for several years -- but that all came to a screeching halt after she talked about her postpartum depression back in 2015 while a guest on "Live! with Kelly and Michael."

The company allegedly wanted to boot her then and there after she walked off stage -- but Hayden said her agent saved her job in the moment.

Still, once her contract expired, she was cut loose ... and her fans haven't forgotten ... or forgiven.

That story -- which Hayden wrote about in "This Is Me: A Reckoning" -- has reignited a firestorm against Neutrogena in the wake of her sudden death ... and social media posts from the company are getting torn apart one by one as people call for a boycott.