Prayer Site Being Covered

The site of Friday's Prayer at the University of Tehran is being covered by a mysterious black tarp. Even though Rafsanjani is not lead the ceremony, it is interesting that the regime is worried about what is going on:

According to sources from within Tehran University, tarpaulin cloths are being used to conceal the site of Friday prayers from those outside the area in which the sermon is actually delivered.

Which begs the question: what is meant to happen at this site which makes it necessary for no one to see through?