The New York State attorney general's office filed a civil lawsuit on Saturday accusing Trump University, Donald J. Trump's for-profit investment school, of engaging in illegal business practices.
The lawsuit, which seeks restitution of at least $40 million, accused Mr. Trump, the Trump Organization and others involved with the school of running it as an unlicensed educational institution from 2005 to 2011 and making false claims about its classes in what was described as "an elaborate bait-and-switch."
In a statement, Eric T. Schneiderman, the attorney general, said Mr. Trump appeared in advertisements for the school making "false promises" to persuade more than 5,000 people around the country — including 600 New Yorkers — "to spend tens of thousands of dollars they couldn't afford for lessons they never got."
The advertisements claimed, for instance, that Mr. Trump had handpicked instructors to teach students "a systematic method for investing in real estate." But according to the lawsuit, Mr. Trump had not chosen even a single instructor at the school and had not created the curriculum for any of its courses.
"No one, no matter how rich or famous they are, has a right to scam hardworking New Yorkers," Mr. Schneiderman said in the statement. "Anyone who does should expect to be held accountable."
The inquiry into Trump University came to light in May 2011 after dozens of people had complained to the authorities in New York, Texas, Florida and Illinois about the institution, which attracted prospective students with the promise of a free 90-minute seminar about real estate investing that, according to the lawsuit, "served as a sales pitch for a three-day seminar costing $1,495."
This three-day seminar was itself "an upsell," the lawsuit said, for increasingly costly "Trump Elite" packages that included so-called personal mentorship programs at $35,000 a course.
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On Saturday evening, Michael Cohen, a lawyer for Mr. Trump, denied the accusations in the lawsuit and said the school had received 11,000 evaluations, 98 percent of which rated students as "extremely satisfied."
George Sorial, another lawyer for Mr. Trump, called the lawsuit politically motivated. He said that Mr. Schneiderman had asked Mr. Trump and his family for campaign contributions and grew angry when denied.
"This is tantamount to extortion," Mr. Sorial said.
Andrew Friedman, a spokesman for the attorney general's office, said that although Mr. Schneiderman had accepted a contribution from Mr. Trump in the past, "the fact that he's still brave enough to follow the investigation wherever it may lead speaks to Mr. Schneiderman's character."