President Donald Trump resumed his Twitter campaign against the Washington Post on Monday, calling the newspaper an “expensive lobbyist” for Amazon.com Inc., which shares billionaire Jeff Bezos as an owner.

“The Amazon Washington Post has gone crazy against me ever since they lost the Internet Tax Case in the U.S. Supreme Court two months ago. Next up is the U.S. Post Office which they use, at a fraction of real cost, as their ‘delivery boy’ for a BIG percentage of their packages,” Trump said in a Twitter posting.

He followed up minutes later: "In my opinion the Washington Post is nothing more than an expensive (the paper loses a fortune) lobbyist for Amazon. Is it used as protection against antitrust claims which many feel should be brought?"

Shares of Amazon fell 1.3 per cent to US$1,789.65 at 9:48 a.m. New York time after dropping by as much as 2.4 per cent after the opening Monday.

Trump has repeatedly attacked Amazon, the Post and its owner, Amazon CEO Bezos. In April, after several attacks on the online retail giant, Trump created a task force to review the business practices of the U.S.Postal Service. Amazon regularly uses the Postal Service to complete what’s called the “last mile” of delivery.

Trump has often said USPS loses money because of Amazon. The Postal Service, legally prohibited from charging shippers less than its delivery costs, disputes the claim.