The Post, citing interviews and legal documents, said the findings suggest the GOP presidential nominee may have violated "self-dealing" regulations. Heads of charitable organizations are not supposed to use nonprofit money on themselves or their other businesses.
The Post previously reported that the Donald J. Trump Foundation has not received a donation from him since 2008. In recent years, the foundation has been primarily funded by donations from other people, the Post reported, citing tax records.
Last week, CNBC confirmed the New York attorney general's office is making inquiries into the foundation to determine whether there has been "some impropriety" regarding the organization's operations.
The Trump campaign said: "The Post's reporting is peppered with inaccuracies and omissions from a biased reporter who is clearly intent on distracting attention away from the corrupt Clinton Foundation, a vehicle for the Clintons to peddle influence at the expense of the American people. Mr. Trump personally and the Trump Foundation, however, are staying focused on their charitable giving to veterans, the police, children and other deserving recipients."
The Clinton campaign released a statement on the Post story. "Clearly the Trump Foundation is as much a charitable organization as Trump University is an institute of higher education," Deputy Communications Director Christina Reynolds said. "Trump's version of charity is taking money from others to settle his own legal issues and buy at least two pictures of himself, which experts say is a clear violation of laws governing charitable organizations. Once again, Trump has proven himself a fraud who believes the rules don't apply to him. It's past time for him to release his tax returns to show whether his tax issues extend to his own personal finances."
UPDATED: This story was updated to include statements from the Clinton and Trump campaigns.
DISCLOSURE: NBC Universal, the parent of CNBC, gave a $500,000 donation to the Donald J. Trump Foundation in 2012.