Trump railed against the e-retailer and The Washington Post — owned by Amazon CEO Jeff Bezos — in a series of tweets Monday morning, claiming the newspaper has "gone crazy" against Trump in the months since Amazon "lost the Internet Tax Case in the U.S. Supreme Court."
Shares of Amazon fell nearly 2 percent in early trading Monday before paring half the losses. The stock closed less than a percent down.
Trump has long called for greater taxes on Amazon, saying in January that the company's dominance is hurting American retailers. Amazon already collects sales tax in every state on the products it sells directly, which account for roughly half of all units sold on its site.
Trump has also repeatedly dinged the company for what he says is an unfair pricing structure with the Postal Service. In April, Trump signed an executive order establishing a task force to look at the operations and finances of the USPS and recommend reforms.
In resurfacing his criticisms Monday, Trump hinted at future antitrust action against the company.
Trump frequently links Amazon to The Washington Post, combining criticism of the newspaper's coverage with claims of unfair business practices by the online retailer.
Earlier Monday, Trump fumed on Twitter about reports that said he wasn't happy with the way talks with North Korea were progressing. The Washington Post reported that Trump asks his aides for daily updates on the negotiations and is frustrated with the lack of rapid progress, as well as coverage of the Singapore summit in June, which yielded no concrete results.
—CNBC's Mike Calia contributed to this report.