The Rotherham 12 Defence Campaign has called a national convention in the run-up to a trial of 12 men for serious offences, including violent disorder.
The 12 were arrested during a 400-strong protest against Nazi group Britain First in Rotherham, South Yorkshire, on 5 September last year.
Police marched it past a pub locals say is known as a haunt of racists. Protesters defended themselves against racist abuse.
The convention, Injustice in the System, has a line-up including Imran Khan, Suresh Grover, Gus John and the Hillsborough Justice Campaign.
The trial is set to start in Sheffield Crown Court on Monday 3 October.
Anti-racists will protest outside.