President Donald Trump again challenged Amazon for using the United States Post Office to deliver its packages at lower shipping costs.

“The post office is losing billions of dollars, and the taxpayers are paying for that money because it delivers packages for Amazon at a very below cost,” Trump said.

Trump cited a study that said Amazon was shipping packages at a discounted rate, costing taxpayers an average of around $1.47 more. (He was likely referring to a 2007 Citigroup study that put the cost at $1.46.)

During these comments at a meeting with Baltic leaders at the White House on Tuesday, the president called the discounted shipping fees a “subsidy” for Amazon that was “not fair.”

He also pointed out that retail companies were losing more business as a result of Amazon.

“You look at some of these small towns where they had a beautiful main street with stores. Those stores are all gone,” Trump said. “That’s a different problem we’re going to have to talk about.”

Trump promised that Amazon would pay more money for shipping in the future.

“Amazon is going to have to pay much more money to the post office; there’s no doubt about that,” he concluded.