The actor's remarks come days after Trump labelled the press "the true enemy of people", Variety reported.
"If you've read anything about the rise of the Third Reich and Adolf Hitler, you will see the parallels. Attacking the media is the first step in the move towards fascism.
"The cornerstone to democracy is an independent, democratic media," Fonda said at the Women's Media Awards.
"And we don't have to take it anymore. Voting is the way to stop it. Everybody has to vote," Fonda said, adding "civility" was also being targeted.
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