Moore stood outside Trump Tower, the presidential hopeful's self-named building in Manhattan, holding a sign emblazoned with the phrase "We are all Muslims" to protest against Trump's most recent controversial comments.

The Celebrity Apprentice star, who is campaigning for the Republican party's presidential nomination, recently suggested followers of Islam should be banned from entering the U.S., and Moore was outraged by the remarks.

He tweeted a picture of himself standing outside Trump's building holding the sign, and added, "Went to Trump Tower & held a sign til the cops came. Then wrote Trump a letter..."

Moore shared an open letter addressed to Trump in which he recalled meeting the aspiring politician on the set of a talk show back in 1998, and the business mogul appeared to be "scared" of the moviemaker.

"I was struck by how you, a self-described tough guy from Queens, seemed like such a fraidey-cat," Moore writes. "You and I went on to do the show. Nothing untoward happened between us. I didn't pull on your hair, didn't put gum on your seat. 'What a wuss,' was all I remember thinking as I left the set.

"And now, here we are in 2015 and, like many other angry white guys, you are frightened by a bogeyman who is out to get you. That bogeyman, in your mind, are all Muslims (sic). Not just the ones who have killed, but all Muslims... In desperation and insanity, you call for a ban on all Muslims entering this country. I was raised to believe that we are all each other's brother and sister, regardless of race, creed or color. That means if you want to ban Muslims, you are first going to have to ban me. And everyone else. We are all Muslim."