Hundreds of members of Yale's Class of 1985 want former classmate Steven Mnuchin to resign as President Trump's Treasury secretary.

In a letter posted online, more than 300 Yale alums said Friday that it's Mnuchin's "moral obligation" to step down from his post. A copy was also sent to Mnuchin's office.

"We call upon you, as our friend, our classmate, and as a fellow American, to resign in protest of President Trump's support of Nazism and white supremacy. We know you are better than this, and we are counting on you to do the right thing," the letter reads.

At a press conference at Trump Tower on Tuesday, the president doubled down on his stance about violence at a rally of white supremacists in Charlottesville, Virginia, claiming many sides were to blame.

Mnuchin was standing next to Trump throughout the presser -- a point of contention for his former peers.

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"President Trump has declared himself a sympathizer with groups whose values are antithetical to those values we consider fundamental to our sacred honor as Americans, as men and women of Yale, and as decent human beings," they said. "President Trump made those declarations loudly, clearly, and unequivocally, and he said them as you stood next to him."

The Treasury Department did not immediately respond to CNNMoney's request for comment.

The letter sought to make clear that its signatories were not being political.

"We can be Republicans, Democrats, Libertarians, Greens, and a number of other things and still be friends, classmates, and patriots, but we cannot be Nazis and white supremacists," it says.

Matthew Countryman told CNN's Brooke Baldwin that he first proposed the idea of asking Mnuchin to resign on Yale's Class of 1985 Facebook page.

The response was "instant," said Countryman, who is a professor of history at the University of Michigan.

"It was really widespread too, that people wanted to find a way for us to express our revulsion," Countryman said.

James Donelan, another classmate who is currently an English professor at the University of California, Santa Barbara, then wrote up the letter.

"Our esteemed classmate was standing next to [Trump]," Donelan said. "That, in itself, is a statement. You can't stand silent when something like this happens. It has to be something you confront."

Countryman, Donelan and others involved are continue to collect names, adding them to the version of the letter that's posted online.

"I hope he hears our message," Countryman said.