Contractor want to cast 2000mmx2000mm inside pile cap(L=3900mm x W=2400mm x h=1800mm) so they can install precast column(800mmx800mm) as per attached photo.
You should be asking this of the engineer who designed or responsible for the design of that footing.
If you are that engineer you should be asking yourself how well will shear transfer across that cold joint. As well as a bunch of other questions which. if you have already performed a thorough design, should be relatively clear.
