About 300 anti-Islamic protesters are expected to rally near Parramatta mosque, calling for it to be shut down following the killing of NSW police accountant Curtis Cheng.
Superintendent Wayne Cox said 75 officers have been deployed to try to keep the Party for Freedom protesters separated from those going to pray.
The group's application to hold a rally was denied by police but Supt Cox said people still had a right to peacefully express their ideas.
The expected demonstration follows the killing of Mr Cheng by a 15-year-old boy who attended the mosque last Friday just before killing the 58-year-old.
The rally is due to start at 5pm and businesses around the area have been warned to be on alert.
A small group of anti-racist supporters has gathered outside the mosque.
