The Derby North MP has launched a crowdfunding project to help him "overturn the unconstitutional decision to 're-suspend' me from the party I love".
He is understood to have lodged papers with the High Court claiming that his suspension is unlawful.
Mr Williamson was initially suspended by Labour in February after being recorded claiming that the party had been "too apologetic" and "given to much ground" on antisemitism.
He was readmitted in June following a disciplinary hearing but was swiftly suspended against after a furious backlash from Labour MPs and Jewish community groups.
The case has now been referred to Labour's main disciplinary body, the National Constitutional Committee.
The party is understood to be confident that its procedures have been followed and that there are therefore no grounds for a successful legal challenge.
Mr Williamson wrote on Twitter: "I've dedicated my life to the Labour Party since I was 19 years-old, and I'm 63 next month. I would hugely appreciate your support in helping to overturn the unconstitutional decision to 're-suspend' me from the party I love. Remember, comrades: UNITY IS STRENGTH!"
The crowd-funding page, set up by the "Campaign for Chris Williamson" reads: "With a heavy heart and after months of personal distress, Chris has been forced to take legal action against the party that he has dedicated his life to. He is challenging his ‘re-suspension’ as unlawful. But to do so, he needs your support.
"This could be a long and costly legal battle. We need your help to cover the immediate costs of the legal case and campaign."
The page says that £75,000 is needed to cover the costs of Mr Williamson's cause but that organisers hope to exceeded that amount to allow them to "begin building a legal fighting fund for the Labour Left, defending other comrades who have been maliciously accused and hounded out of the party".
It adds: "Capitulation is complicity. Solidarity is sacred. Defend your comrades."
A Labour spokesperson said: "Chris Williamson is suspended from the Labour Party pending a hearing of the National Constitutional Committee, Labour's highest disciplinary body. We do not give a running commentary on individual cases."
Mr Williamson has been contacted for comment.