In comments translated by the news-wire, Mr Demeter wrote that Europe was “George Soros’ gas chamber” and compared the philanthropist to Adolf Hitler, saying he was “the liberal Führer, and his liber-Aryan army deifies him more than did Hitler’s own”.
The Federation of Hungarian Jewish Communities (MAZSIHISZ) said the remarks were “tasteless and unforgivable” and a “textbook case of Holocaust relativism.”
The country’s Democratic Coalition called for Mr Demeter’s firing.
“A man like him has no place in public life, not just in a European country but anywhere in the world,” the party said in a statement.
In a Facebook post addressed to prime minister Viktor Orbán, former leader Gordon Bajnai said he would feel “ashamed” were Mr Demeter not removed from his government post by Monday.
Mr Soros is a Hungarian-born Holocaust survivor and philantropist. He is a frequent target of conspiracy theories from the far-right and often the subject of attacks from Mr. Orban's government.