amazon box
Amazon boxes are seen stacked for delivery in the Manhattan borough of New York City, January 29, 2016. Reuters/Mike Segar

Amazon shares dropped 4 percent on Monday after US President Donald Trump lambasted the online retailer. The president tweeted on Monday about the pricing of its deliveries through the United States Postal Service (USPS).

“Only fools, or worse, are saying that our money losing Post Office makes money with Amazon,” Trump tweeted. He added that “fully taxpaying retailers” are closing stores all over the US, arguing that it is not a level playing field.

The POTUS has been expressive of his views about the company’s use of the Postal Service. Details of Amazon's payments to the US Postal Service are not publicly known. Wall Street analysts estimated that it pays the USPS roughly half of what it would to FedEx Corp or United Parcel Service Inc to deliver a package.

DA Davidson analyst Tom Forte wrote that Trump’s comments are consistent with industry sources they have spoken to. “An argument, however, could be made that the USPS was losing billions before it expanded its service offerings for Amazon and would, still, likely lose billions if Amazon discontinued its use of the USPS tomorrow,” Forte added.

Trump earlier accused Amazon of not paying enough tax but so far offered no evidence to back up his comments. Amazon shares have gained almost 20 percent this year, helping the company’s market value reach about $700 billion.

Amazon Chief Executive Jeff Bezos privately owns The Washington Post, which won a Pulitzer Prize last year for its investigation of the POTUS’ donations to charities. White House Deputy Press Secretary Raj Shah has said that Trump's comments were not a personal grudge but were a matter of policy.

Other companies recorded a loss this week. Monday saw stocks fell sharply as investors responded to trade tensions between the United States and China, the latter having imposed $3 billion of tariffs on US farm goods and other exports.

At the same time, some huge technology companies face scrutiny. Facebook dropped amid a privacy situation that continued to weigh on its stock.

In Australia, Amazon made its first major play in February with the rollout of Fulfilment by Amazon (FBA). The service offers free delivery on eligible orders above $49.

Amazon Australia is slowly ramping up its assault on the Australian retail sector. Based on research from Morgan Stanley last month, the price discount between Amazon and major Aussie retailers was getting larger for a number of goods, Business Insider Australia reports.