Attorneys for Pharrell Williams sent President Donald Trump a “cease and desist” letter denouncing the use of the artist’s song “Happy” at an event Trump headlined on Saturday, mere hours after the deadly mass shooting at a Pittsburgh synagogue.

“On the day of the mass murder of 11 human beings at the hands of a deranged ‘nationalist,’ you played his song ‘Happy’ to a crowd at a political event,” read the letter sent Monday, first reported by The Hollywood Reporter. “There was nothing ‘happy’ about the tragedy inflicted upon our country on Saturday and no permission was granted for your use of this song.”

On Saturday, a gunman shot up a Pittsburgh synagogue, killing 11 people in what is likely the deadliest anti-Semitic attack in U.S. history. The suspect, 46-year-old Robert Bowers, had a history of posting racist and anti-Jewish statements online and reportedly yelled during the attack, “All Jews must die.”

After the attack, Trump called out the “evil Anti-Semitic attack” as an “assault on humanity.” Later that day, the president went ahead with plans to attend two events, a Future Farmers of America Convention in Indiana ― where he joked about having a “bad hair day” ― and a rally in Murphysboro, Illinois.

The letter from Pharrell’s lawyers said the artist “has not and will not” allow Trump to “publicly” play “any of his music” and asked that he “cease and desist from any further unauthorized use.”

Pharrell isn’t the first artist to demand their songs not be played at Trump’s events. In 2016, British rock band Queen denounced the Republican National Convention’s use of their song “We Are the Champions” to introduce then-nominee Trump. And earlier this year, Steven Tyler of Aerosmith also sent a letter demanding the president stop playing the band’s songs at rallies.