The Republican presidential nominee argued that Slim, a shareholder of The New York Times and a donor to the Clinton Foundation, is trying to undermine Trump's candidacy.
"We're going to let foreign corporations and their CEOs decide the outcomes of the — you just can't do this. We can't let this happen. We are not going to let it happen where they decide the outcome of our elections," he said at a rally in Greensboro, North Carolina.
Slim, however, does not own voting shares, just common shares of the Times. The Mexican billionaire is the largest minority shareholder, but does not appear to own any of the powerful voting shares that would allow him to influence the Times' operations.
Trump's allegations feed into his unproven claims of a rigged election system and "false smears" that he says are part of a conspiracy bent on defeating him. A representative for Slim, however, said that the Mexican billionaire doesn't have any interest in influencing the election.
Trump also lashed out at Times reporters and said, "they're not journalists," but instead "corporate lobbyists for Carlos Slim and for Hillary Clinton."
Times publisher Arthur Sulzberger Jr. said in a statement, "Carlos Slim is an excellent shareholder who fully respects boundaries regarding the independence of our journalism. He has never sought to influence what we report."
On Wednesday, the Times published a story which details claims that Trump made inappropriate advances on two women years ago. NBC News has not confirmed the allegations. Trump vociferously denied those allegations, calling them "totally and absolutely false."
—CNBC's Michelle Caruso-Cabrera and Steve Kopack, and Reuters contributed to this report.