President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE on Tuesday complained about “unfair” tax laws that favor online retailers, as the Supreme Court hears arguments in a case over the subject.

“States and Cities throughout our Country are being cheated and treated so badly by online retailers. Very unfair to traditional tax paying stores!” Trump tweeted.

States and Cities throughout our Country are being cheated and treated so badly by online retailers. Very unfair to traditional tax paying stores! — Donald J. Trump (@realDonaldTrump) April 17, 2018

The Supreme Court on Tuesday heard oral arguments in the case of South Dakota v. Wayfair, which centers on a South Dakota law that requires certain out-of-state online retailers to collect the state’s sales taxes.

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South Dakota asked the Supreme Court to uphold its law and to overturn a 1992 ruling that prevents states from compelling businesses to remit their sales taxes unless the business has a physical presence in the jurisdiction.

The state of South Dakota argued that it is losing out on significant sales tax revenue, and that the old law provides online retailers an advantage over brick-and-mortar stores inside state lines.

Representatives for Wayfair argued that implementing the new law would increase sales tax costs and create barriers for small businesses looking to compete with larger retailers.

Trump earlier this month attacked Amazon on Twitter, claiming that the online retailer was at fault for the U.S. Postal Service's declining revenues. He has since commissioned a panel to examine the Post Service's operations and business model.