Blades Independent Fans Association chairman Richard Batho told the Sheffield Star: "Hopefully fans from both clubs - United and Wednesday - will turn out because this has the power to affect everyone.
"The more people who turn out, the better. We need to get across the message that football fans in general aren't prepared to stand by when something like this happens.
"United supporters must attend in numbers, but it would be great to think everyone from the region, whether they follow us, Wednesday, Rotherham, Barnsley, Doncaster or Chesterfield, will also lend us their backing. It really is that important."