The 2012 star upset autism activist Jenny McCarthy and Autism United officials in 2008 when she called them "parasites" for leading a campaign to overhaul America's immunisation programmes, claiming vaccinations are largely responsible for autism in children.
McCarthy, who is the mother of an autistic child, led a rally in Washington, D.C. calling for the Federal Government to clean vaccines of all toxins and to change a loaded schedule of immunisation, which experts claim leads to the cause of autism.
The cause is controversial because leading medical groups insist there's no clear proof that vaccinations lead to autism.
Peet agrees with the medics, but she has apologised for her emotional outburst in a magazine interview.
Now a celebrity spokesperson for child welfare group Every Child By Two and the Measles Initiative, Peet has sparked the debate again as she prepares to become a pre-school mum.
She tells Self magazine, "It scared me when I learned how many parents were withholding vaccines from their children. It made me frightened of the possibility that some of these diseases are coming back.
"This is about the future of our children's health. It's about what happens when you become complacent and you're not vigilant as a community."
And she insists the statistics speak for themselves: "I learned that every day 540 children around the world die from measles when there is an absolutely safe vaccine that costs less than a dollar per child.
"My daughter is about to go to pre-school. If you walk by a school and you try to imagine 540 children... it's unconscionable that we're not getting the vaccines to people."
Peet's latest remarks are sure to upset McCarthy, who still hasn't forgiven the actress for the comments she made in 2008. She said, "She has a lot of balls to come forward and be on that side, because there is an angry mob on my side. I like the fact that I can say she's completely wrong... Until she walks in our shoes she has no idea."
And Autism United bosses are still calling on supporters to boycott Peet's films.
Executive director John Gilmore raged, "Ms. Peet's comments are deplorable and an apology will not suffice."