The Charmed star and more than 40 celebrities signed a letter sent to Georgia Governor Brian Kemp opposing a new law that would ban abortions in the state after six weeks, or when a feotal heartbeat is detected.
Defending her decision, Milano tweeted: "I love God. I believe in God.
"But I don't believe my personal beliefs of which we can't confirm should override scientific facts and what we can confirm.
"'If I have told you earthly things and you do not believe, how can you believe if I tell you heavenly things?' John 3:12."
The tweet was liked more than 28,000 times but it also sparked a lot criticism.
You don't have to love God to acknowledge the irrefutable science that a unique, individual human life begins at the moment of conception.— Lila Rose (@LilaGraceRose) April 1, 2019
But if you love God, then you also will love His children. He's a father, and every single one of us are created in His image.
Author and speaker Allie Beth Stuckey tweeted in reply: "This tweet shows that you have very little knowledge of both theology and science."
The so-called "feotal heartbeat" bill, passed by Georgia lawmakers last week, is among the most restrictive abortion bans in the country. The current state law allows abortions up to the 20th week of pregnancy.
7. There is a huge difference between pro-life and anti-choice and forced pregnancy. I'd like to think everyone is pro-life.— Alyssa Milano (@Alyssa_Milano) March 29, 2019
But don't you dare try to strip away the rights of millions of women because of your own religious beliefs or political ideology.
Celebrities including Alec Baldwin, Amy Schumer, Rosie O'Donnell, Sean Penn, Mia Farrow and Ben Stiller have joined Milano in their condemnation of the pro-life bill.
After more than 15,000 comments under her controversial tweet, Milano reasserted her position by tweeting: "Abortion is a decision to be made by a woman and her physician (and potentially her God if she's religious).
"It is not for the government to decide and it certainly is for no one to judge. #Trustwomen We will make the right choice for her health and her unique situation."
Stay up to date with the latest news stories from a Christian perspective. Sign up to our daily newsletter and receive more stories like this straight to your inbox every morning.