After a week of major retailers dropping Ivanka Trump’s products, the #GrabYourWallet boycott made its biggest impact ever today when it prompted the president of the United States to respond with an angry tweet that may have crossed an ethical line, say government ethics experts.

This morning, just 20 minutes into a national security briefing in the Oval Office, President Trump went on Twitter to take a swing at Nordstrom, which announced last Thursday that it would no longer sell Ivanka Trump products: “My daughter Ivanka has been treated so unfairly by @Nordstrom. She is a great person — always pushing me to do the right thing! Terrible!” Within seconds, the share price of the retailer, which attributed its decision to the brand’s poor performance, dipped for a few minutes before quickly recovering. Later, the official @POTUS account retweeted Trump’s tweet, a possible ethics violation which illustrates the conflicts of interest inherent in the real-estate mogul’s new role as the president.

Nordstrom’s decision last week turned out to be a tipping point. The next day, Neiman Marcus said it would no longer stock items from the Ivanka Trump Fine Jewelry collection. (There are now rumors that the collection may be discontinued altogether.) Also employees at T.J. Maxx and Marshalls reportedly received an unusual memo last week instructing them to remove Ivanka Trump signs and hide products among other merchandise on racks. This week, Belk department store, Jet, and Shopstyle all dropped her products.

Since he was elected, Trump and his daughter, who serves as one of his closest advisors, have been under pressure to divest themselves from their businesses to address concerns that they could wield the levers of government to advance their own companies or to be influenced by special interests. But the Trumps haven’t gone that far. The president handed over control of the Trump Organization to his two oldest sons but retains ownership of the company through a trust and will benefit financially from his sons’ business deals.

Ivanka herself made a public show of separating herself from her company last November and in January, she announced on Facebook that she would take a formal leave of absence from both the Trump Organization and her own brand. But it’s clear that the Trump family has been closely watching the brand’s fate. Maggie Haberman, the New York Times White House correspondent, said that sources close to Ivanka claimed she was upset by Nordstrom’s decision.

The tweet and especially the retweet raised plenty of concerns among lawyers and ethics experts. “This is not trivial,” says Kathleen Clark, a law professor at Washington University who is an expert of government ethics, told Fast Company. “Trump is using government power for his personal purposes. That’s why we all wanted him to divest. He refused to and here he is using government power for his financial benefit or the financial benefit of his daughter.”

What are the legal implications of his decision? It’s complicated.