Early Thursday morning, President Donald Trump began to wage war on an enemy the United States has never battled: Amazon.com. Continuing through Monday, the president attacked the e-commerce retailer for its effect on the United States Postal Service.

“I have stated my concerns with Amazon long before the Election.” Trump tweeted. “Unlike others, they pay little or no taxes to state & local governments, use our Postal System as their Delivery Boy (sic)… and are putting many thousands of retailers out of business!”

The president did not say not announce his source for claiming that Amazon was withholding tax information. However, according to Fortune, the company saw its share prices fall by 3.9 percent. The S&P Index was also down 0.6 percent.

The Washington Post noted Monday that Amazon collects sales tax in all 45 states which legally require it on products they sell. The Post also pointed out that Amazon founder and CEO Jeff Bezos owns the paper itself. It, however, runs independently from any retail operations.

Some have stated that Amazon’s expansion in the marketplace is why it pays so much in taxes. CNBC stated that in Amazon’s infancy, they were not obligated to collect sales tax because the brand was so small. Since expanding, Amazon’s sales tax collection rate has gone up equally. However, these rules only apply to transactions with the company itself; third-party sellers have different sales tax requirements.

The president’s claim about Amazon’s misuse of the Postal Service has been questioned, as well. According to the independent fact-checking organization, Politifact, the USPS lost $2.7 billion in 2017. In spite of this, parcels brought in 28 percent of Post Office revenue.$7 billion of the $19 billion the Post Office took in on parcel shipments came from Amazon and its marketplace.

Many brick and mortar retail stores feel Amazon’s impact on sales and growth. In late March, Toys ‘R’ Us announced it would be closing all its U.S. locations and shutting down its website. According to Time, the only major toy seller left is Amazon, whose toy sales grew nearly 12% in 2017.

As a result of the financial impact, many chains offer “price match guarantees.” Electronics distributors, grocers, and outlet stores have all begun to lower their price at the register to match Amazon. Retailers such as Best Buy and Walmart match prices on all items sold and shipped by Amazon. Still, price match is only available by customer request, and is subject to exceptions such as Black Friday deals.

Neither Amazon nor the United States Postal Service have issued a statement in response to President Trump at this time.