We are changing an existing shower from a 32x32 fiberglass to a 48x48 tiled in shower.
There is a cast iron Pipe that was connected to a copper vent. It now sits in the middle of the larger area we are intending to be our shower. The vent pipe that it was connecting to is less than 30" away can we just chisel down and cap the old vent. And what would be the possible problems if we did so.

Probable problems would be a shower trap that is not vented and when you flush the toilet the shower trap water is pulled out.