During his keynote address at the National Rifle Association's annual convention in Texas, Mr Beck targeted the New York mayor for robbing US citizens of 'responsibility' and subjecting them to a dictator-like regime.
Both the Anti-Defamation League and Jewish organisation, B'nai B'rith, were upset by Mr Beck's comments and called for an apology.
A spokesman for B'nai B'rith told ABC News: 'Glenn Beck, the keynote speaker at the NRA's annual convention, trivializes the Holocaust when he compares New York City Mayor Michael Bloomberg to Adolf Hitler.
'The casual use of Nazi imagery or words serves to undermine the atrocities of the Holocaust. Glenn Beck should apologize.'