According to Newsweek
, Trump Hotel executives visited the communist-run island in 1998 to meet with officials there about doing business.
The company spent over $68,000 on the trip and does not appear to have obtained the necessary US treasury license to spend money in Cuba, Newsweek reported.
"They clearly knew what the rules were and flouted them," the article's author, Kurt Eichenwald, said on CNN's "New Day."
The Trump campaign did not respond to CNN requests for comment. But on ABC's "The View," Trump campaign manager Kellyanne Conway denied he had broken the law.
"He's very critical of Cuba. He's very critical of (Fidel) Castro," Conway said. "We're talking about did his hotel invest money in 1998 in Cuba? No."
She later tweeted
, "For those getting hard news fr. @TheView, biz officials tell me Trump: 1) did no biz in Cuba 2) respected embargo 3) was critical of Castro."
Under the five-decades-old trade embargo -- which can only be lifted by Congress -- US citizens are banned from spending any funds on the island.
The US and Cuba restored relations last year and President Barack Obama has eased some sanctions to allow more US travel and commerce with Cuba. At a rally in Miami earlier this month
, Trump blasted the Cuba policy changes, an apparent shift from past statements
in which he supported the reopening of diplomatic relations after more than 50 years.
"All of the concessions that Barack Obama has granted the Castro regime were done through executive order, which means the next president can reverse them and that's what I will do if the Castro regime does not meet our demands," Trump said.
The Republican candidate said he could close down the newly reopened US embassy in Havana if Cuba didn't allow greater political and religious rights for Cubans.
But a Cuban Foreign Ministry official on Wednesday said the island's government would not respond to Trump's demands.
"Cuba has always made clear that Cuba's internal matters aren't on the negotiating table," Gustavo Machín, the Foreign Ministry's subdirector for US affairs, said at a press conference here. "They're a function of internal decisions by Cuba and the Cuban people."
For decades, the Cuban-American community has been reliably in the GOP camp and often swung Florida elections to Republican candidates. But in recent years, observers say a generational shift is taking place, and a Florida International University poll
of Cuban Americans in Miami-Dade County earlier this month found a majority now support lifting the embargo.
The same survey found 35.5% of Cuban-Americans favor Trump to 31.4% for his Democratic challenger, Hillary Clinton.