Little Mix, Nile Rodgers, Lewis Capaldi and Rita Ora are among the stars calling for an end to racism.
"We are at our worst when we attack one another," the letter said.
It cited recent "anti-Jewish racism", after grime artist Wiley shared anti-Semitic posts. Wiley later apologised.
Hundreds of representatives from the music industry co-signed the letter, which says they want to show "that love, unity and friendship, not division and hatred, must and will always be our common cause".