Fresh off the nation’s biggest holiday shopping season in years, President Trump went postal on Amazon, suggesting on Twitter the online retailer is taking advantage of the federal government’s beleaguered mail service.

Amazon and its founder, Jeff Bezos, have been the targets of Trump’s tweets in the past, but his Friday morning barrage did collateral damage to the U.S. Postal Service, which Trump said ought to charge more to deliver the online giant’s packages.

“Why is the United States Post Office, which is losing many billions of dollars a year, while charging Amazon and others so little to deliver their packages, making Amazon richer and the Post Office dumber and poorer? Should be charging MUCH MORE!” Trump tweeted.

His comment seems to be in response to a “Fox & Friends” segment about tech trends in the new year which was aired Friday morning. The piece focused on Amazon making shopping easier for its customers.

Following the president’s comments, Amazon shares quickly reversed course in premarketing trading.

This isn’t the first time Trump’s used Twitter to taunt Amazon.

The president has a long-standing feud with the online retailer and especially its founder Jeff Bezos.

Bezos also owns The Washington Post, a frequent critic of the president.

Bezos saw his net worth climb to more than $100 billion in November after shares of Amazon surged.