Supporters of Jeremy Corbyn have suggested that the judge in the Labour membership case may have been influenced by his "Zionist" background.
Lord Justice Jack Beatson ruled in the Court of Appeal on Friday that Labour had the right to block new members from voting in the leadership contest between Jeremy Corbyn and Owen Smith.
The decision affects around 130,000 party members, most of them thought to be Corbynites.
Mr Corbyn's campaign team attacked it as wrong "both legally and democratically".
After the ruling, messages were posted on Twitter questioning Justice Beatson’s competence because he was "born in Israel".
A tweet from the account of Davidgeorgeking, a Corbyn supporter, said: “I don't know if this is true but the appeal court judge in Labour V Labour case today was (I'm told) born in Israel!”
The tweet cited a post from Ian R Millard referring to a “cuckoos in the nest Israel lobby”.
The account in the name of Ian Millard includes photos of Adolf Hitler and a message backing National Socialism.
In response, tweets from the account of a Leicester man called Safraan, said the judge "was born in Haifa- Israeli occupied Palestine”, adding: “Its quite apparent that Beatson, LJ. is a Zionist!” and using the slur term “Zio”.
The tweets also noted that the judge “went to a Jewish boarding school”.
Some Twitter users reacted by saying the implication that the judge’s independence had been compromised was “antisemitic”.
But another tweet from Davidgeorgeking claimed: “No, it is a legitimate question - Was/is he being influenced by a current pro/anti-Palestine/Israel argument?”
Safwaan retweeted a post in the name of David Shayler, seemingly the former MI5 officer who was prosecuted under the Official Secrets Act for leaking state secrets. The tweet said that Justice Beatson’s decision was “ more evidence legal system is Zionist and of the lengths they will go to to stifle an opponent” such as Mr Corbyn.
Lord Justice Beatson has sat on the Appeal Court bench since 2013. Previously he was a High Court judge and is considered one of the foremost members of the judiciary.
The case came before him after the High Court backed Labour members who challenged the decision by the party’s National Executive Committee that six-months’ continuous membership was required to vote in the leadership election.
Announcing his decision, the judge said: "On the correct interpretation of the party rules, the National Executive Committee has the power to set the criteria for members to be eligible to vote in the leadership election in the way that it did."
