President Donald Trump took to Twitter for the fourth time in one week to bash e-commerce company Amazon on Tuesday.

This time, the president reinforced his assessment that Amazon's business is costing taxpayers "many billions of dollars" through subsidized rates at the United States Post Office.

tweet

"I am right about Amazon costing the United States Post Office massive amounts of money for being their Delivery Boy," Trump tweeted. "Amazon should pay these costs (plus) and not have them bourne [sic] by the American Taxpayer."

Shares of Amazon declined after the president's tweet and briefly turned negative on the day. The stock rebounded later in the day, closing up 1.46 percent at $1,392.05.

Asked to clarify his views later in the day, Trump said that the existing service practically gives Amazon a government subsidy.

"You have retailers all over the United States that are going out of business," Trump said. "If you look at the cost that we're subsidizing, we're giving a subsidy to Amazon."

The president has claimed in prior Twitter messages that the Post Office loses "a fortune" thanks to Amazon's large shipping volumes while the company benefits from the government's postal service.