The president-elect's choice of Bannon -- chair of the pro-Trump news platform Breitbart and a key figure in his victorious election campaign -- has raised a chorus of protests to which Sanders forcefully added his voice.
"The appointment by President-elect Trump of a racist individual like Mr. Bannon to a position of authority is totally unacceptable," the Vermont senator said in a statement.
Sanders, who lost to Hillary Clinton in the Democratic primary, said decades of work toward making the United States a more tolerant society were at stake.
"This country, since its inception, has struggled to overcome discrimination of all forms: racism, sexism, xenophobia and homophobia," he said.
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"We are not going backward," he warned. "In a democratic society we can disagree all we want over issues, but racism and bigotry cannot be part of any public policy," Sanders warned.
"The appointment of Mr. Bannon by Mr. Trump must be rescinded."
Trump's camp rejects any suggestion that Bannon is a bigoted extremist, saying critics should look at his full resume -- and emphasizing his record as a former naval officer, Goldman Sachs managing partner and Hollywood producer.
Trump named the anti-establishment firebrand at the same time as he appointed top Republican Reince Priebus as his White House chief of staff, blending pragmatism with a rabble-rousing edge in the first appointments of his new administration.
