He wrote: "Solidarity now would be appreciated."
Labour MP Neil Coyle replied: "Getting in the sea would very much appreciated."
He then clarified that he meant Mr Williamson was "a sh*t".
Labour MP Rachel Reeves listed alternative uses for the money people might donate to a crowdfunder for Mr Williamson, then said: "Or you could help get someone the party has concluded brought us in to disrepute back in. Tough choices."
The National Constitution Committee is Labour's highest disciplinary body and has the power to expel members.
Mr Williamson was briefly allowed to return to Labour in June but was then resuspended following an outcry.
He was branded a "Jew baiter" last December by then-Jewish Labour Movement chair Ivor Caplin, after Mr Williamson signed a petition in support of notorious antisemite Gilad Atzmon, for which he later apologised.
Mr Williamson was not suspended over the Atzmon petition, despite calls for it to happen.
