"This (Washington Post) is owned as a toy by Jeff Bezos, who controls Amazon. Amazon is getting away with murder tax-wise. He's using the Washington Post for power so that the politicians in Washington don't tax Amazon like they should be taxed," Trump said.

In an interview on Fox News, the presumptive GOP presidential candidate also said Amazon Chief Executive Jeff Bezos , who owns The Washington Post, is using the newspaper to influence politicians in Washington to help Amazon on taxes.

"He's using the Washington Post ... for political purposes to save Amazon in terms of taxes and in terms of antitrust," Trump said.

"He thinks I'll go after him for antitrust. Because he's got a huge antitrust problem because he's controlling so much, Amazon is controlling so much of what they are doing," Trump said.

However, antitrust violations involve some level of illegality, not just a large market share, said Seth Bloom, former general counsel of the U.S. Senate's Antitrust subcommittee, on CNBC's "Closing Bell."

"Amazon has become a very efficient producer and has delivered many benefits to consumers," he said. "That's what really is the test here, is whether the conduct of Amazon is benefiting or harming consumers. And I haven't heard anything said about how Amazon is harming consumers."

Amazon should still be wary of an investigation, warned Andrew Stoltmann, an attorney who represents victims of investment fraud. "Amazon shouldn't take these statements from Donald Trump so lightly, because once you get the DOJ, once you get the FTC looking at you, there could potentially be problems," he said.

Amazon did not immediately respond to a request for comment.