In an open letter to Mr. Trump, Wharton backers wrote that they have been “deeply disappointed” in his candidacy and “outraged that an affiliation with our school is being used to legitimize prejudice and intolerance.”

“Although we do not aim to make any political endorsements with this letter, we do express our unequivocal stance against the xenophobia, sexism, racism, and other forms of bigotry that you have actively and implicitly endorsed in your campaign,” said the letter, which was posted to Medium.com and as of Monday morning carried the signatures of about 2,000 Wharton students, alumni, faculty members and other supporters.

For Mr. Trump, a 1968 graduate who saw some of his children later follow him to the school, Wharton has long held a special significance to him as the educational beginnings of his career in real estate. And it’s a credential that he has used to promote his intelligence, often remarking about how only the best students are accepted.

Mr. Trump’s campaign spokeswoman did not respond to a request for comment on the letter. He has disputed assertions that he is prejudiced, saying that he is the “least racist person there is.”