Here’s a telegram the great conductor Erich Kleiber send to Milan in December 1938:
I learn at this time that the Teatro alla Scala has closed its doors to your compatriot Israelites. The music is made for all as the sun and air. Where you deny to human beings this source of consolation so necessary in these times so hard and this only because they belong to another race or religion, I can’t work either as a Christian and as an artist. I must therefore ask you to consider null and void my contract despite the pleasure I had in directing in this magnificent theater that recalls the most noble traditions of Italy. Erich Kleiber.
h/t: Tomislav Vichev