Sensible Sentencing Trust Rotorua area co-ordinator Maggie Bentley said they were expecting thousands of people at the Rotorua march.
Those taking part will meet at the Village Green at 9am. There will be a few speakers before the march travels down Fenton St and on to Arawa St, assembling outside the Rotorua court.
"There will be marches happening all around the country but Rotorua, being the place where the pair are being sentenced, is the main march and is expected to be the biggest."
She said she believed there would be a gang presence in the march, though she did not know which gangs would be involved.
"We don't want any trouble and I understand there will be extra police presence in and around the courthouse. We are marching for two main reasons - to show we are against the killing of our children in New Zealand and our opposition to plea bargaining.
"[Shailer and Haerewa] killed Moko, there is no other way about it, he was murdered, plea bargaining is rubbish."
Meanwhile, Attorney-General Christopher Finlayson has announced he will explain the decision to downgrade the charges after Shailer and Haerewa are sentenced.
When the Ministry of Justice was asked by the Rotorua Daily Post whether additional security measures were being put in place for the sentencing and protest, a spokesman said they would not discuss security arrangements.
"Generally speaking, court security assessments are routinely carried out and any risks identified will see additional security measures put in place. Our priority is to always ensure the safety of all those who come to the courthouse."
He said they expected a lot of people would want to attend the sentencing. "With limited seating and space available in the courtroom's public gallery, priority will be given to whanau and supporters of those involved in the case."
Police spokesman Nicholas Barkley said police would not comment on the specifics of any operation that was ongoing.