When the Hungarian State Opera’s white cast of singers came together in Budapest earlier this month to revive a production of George Gershwin’s opera “Porgy and Bess,” they received letters carrying an unusual request: to declare themselves African-American.

According to the Hungarian news website Index, which said it has seen a copy of the letter, the singers were asked to sign a declaration stating that “African-American origins and spirit form an inseparable part” of their identity. At least half the group signed, according to Index.

The letter was from the Hungarian State Opera’s general director, Szilveszter Okovacs, who last year defended the company’s decision to perform the work with white singers against the wishes of the Gershwin estate.

“Porgy and Bess,” which premiered in the United States in 1935, tells the story of an African-American community’s struggles with violence and racism. George Gershwin famously turned down companies that wanted to perform the opera in blackface, and his estate stipulates that the work should be performed by an all-black cast.