US postal workers union endorses Bernie Sanders for president in 2016
Bernie Sanders has taken a slim lead over Democratic presidential frontrunner Hillary Clinton in Iowa, while Donald Trump extended his domination over the rest of the Republican field, polls show (AFP Photo/Jim Watson)

The U.S. postal workers union's executive board said on Thursday it had voted to endorse Bernie Sanders for the Democratic presidential nomination in 2016, the union said in a statement.

The endorsement was a setback for Democratic frontrunner Hillary Clinton, who has been vying with Sanders, her chief rival, for the support of organized labor.

"Politics as usual has not worked. It's time for a political revolution," said Mark Dimondstein, president of the postal workers union. Dimondstein called Sanders, a U.S. senator from Vermont, "a true champion" of workers.

(Reporting by Caren Bohan; Editing by Toby Chopra)