President Donald Trump waded into a longstanding scrap between online retailers and their brick-and-mortar rivals with a tweet Wednesday about Amazon.com Inc. and taxes.

And he has a point, retail industry specialists say, though the online giant has taken steps to reduce its tax advantage in recent years.

Amazon began collecting sales taxes on purchases in all states that levy them earlier this year, despite an exemption that allows online retailers to avoid collecting them in places where they don't have a physical presence. But the company still avoids charging shoppers sales taxes when they buy from one of its third-party vendors — sales that make up about half the company's volume.