The Unite union's Andrew Murray is demanding damages for libel over a story that appeared in the Mail on Sunday.
Murray, chief of staff of Unite, is suing publishers Associated Newspapers over a 1 April story headlined 'Red Len's right-hand man â€¦ the hardline â€˜Member for N Korea'".
Murray argues the story was defamatory and said he endorsed criminal violence against police, justifying attacks during last summer's riots.
The story also claimed he had expressed sympathy for terrorist attacks carried out by suicide bombers including the murder, maiming and injury of victims of the 7/7 bombings in London, he claims.
Murray says the story has injured his reputation and caused him embarrassment and distress.
He is also seeking aggravated damages, saying the newspaper dishonestly misrepresented the circumstances in which he gave a speech at a rally that appeared on YouTube.
He says the Mail on Sunday falsely claimed what he had said to the rally had only just come to light, and suggested the speech was only being made public because a video of it had been passed to the Mail on Sunday.
This, he claims, falsely cast him in a sinister light and actively prevented readers from judging for themselves what he actually said, by concealing the fact that his videoed speech was on YouTube.
Murray accuses the Mail on Sunday of distorting what he had said about the 7/7 suicide bombers so that it appeared he had made a comment sympathising with their murderous actions, taking his words out of context and deleting obviously crucial words which suggested the contrary.
He was given no chance to correct or respond to the allegations before publication, a High Court writ says.
Email email@example.com to point out mistakes, provide story tips or send in a letter for publication on our "Letters Page" blog