The great Gaon of Vilna sat with voice but no vote on the Council of the Jews of Vilna. His task was to comment from a Torah perspective on new legislation proposed before the Council. When there was no such new legislation, he did not take part in the meeting.
One day a member of the Council put forward a proposal for greatly reducing the influx of Jews from poorer regions into Vilna, where they hoped for a better life. The Gaon rose to leave the meeting. "But Rabbi," said a Councilmember, "we need your comment on this proposed new legislation!"
"What new legislation?" said the Gaon. "This was already the law of Sodom, long ago!" And he left.
The proposal was dropped.
Is this story documented anywhere?