President Trump came under fire Saturday for a tweet about Trump International Golf Links, the golf course he owns in Aberdeen, Scotland.

On Feb. 26, the Trump Organization tweeted a photo of the course along with a quote from architect Martin Hawtree: “The landscape framework of @TrumpScotland comes close to an ideal. There is nothing missing & there are no weak holes.”

President Trump re-tweeted the praise with his own comment on Saturday: “Very proud of perhaps the greatest golf course anywhere in the world. Also, furthers U.K. relationship!”

Ethics experts pointed to this remark as a violation of the Constitution’semolument’s clause, which is described in Article 1, Section 9: “No Title of Nobility shall be granted by the United States: And no Person holding any Office of Profit or Trust under them, shall, without the Consent of the Congress, accept of any present, Emolument, Office, or Title, of any kind whatever, from any King, Prince, or foreign State.”

According to the Washington Post, “Historians largely agree that the original intent of the constitutional provision was to discourage early American leaders from being influenced by gifts or titles bestowed by European governments or royalty.”

Following Trump’s tweet, government watchdogs were quick to cite an apparent conflict of interest. Walter Schaub, the former director of the U.S. Office of Government Ethics, called Trump’s tweet his “most explicit commingling of personal interests and public office to date. … This is the tone from the top that leads his appointees to violate ethics rules.”

“There it is,” tweeted Citizens for Ethics. “The president is using an official statement as an ad for his business and making sure everyone knows he ties his business to US relationships with foreign countries.”

Brianne Gorod, chief counsel at the Constitutional Accountability Center, also weighed in: “The Framers adopted the Foreign Emoluments Clause because they were deeply concerned that the nation’s leaders might put their financial self-interest above the national interest,” she tweeted.

Trump’s love of golf and pride in his course portfolio is well documented. In February, the President teed it up with Tiger Woods and Jack Nicklaus. He also made headlines for installing a new simulator in the White House.