In a cease and desist letter sent Monday, Williams' attorney Howard King called on the President to stop playing the hitmaker's song "Happy" during events. The song was played at a rally over the weekend just hours after a gunman killed 11 people 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 in Indiana," King wrote in the letter. "There was nothing 'happy' about the tragedy inflicted upon our country on Saturday and no permission was granted for your use of this song for this purpose."

King claims the use of "Happy" without consent constitutes both copyright and trademark infringement.

"Pharrell has not, and will not, grant you permission to publicly perform or otherwise broadcast or disseminate any of his music," King wrote.

This is not the first time Trump has received flak from angry musicians after using their music without permission. The Rolling Stones, The O'Jays, Adele, Queen and several others have asked Trump to stop using their music as well.