Occupation of common area in apartment floor..

Respected all..

I have a query regarding the common areas in Apartment floor.

I am residing in an apartment where there are 5 flats per floor. In our floor there are three common areas where one common area is in between two flats.

The owners of the two flat put a gate at the beginning of the common area and telling Builder said to keep the gate at the time of purchase of flat. And we have no access to move in to see outside and they are using it like a personal room.

My question is, is it correct thing to privatize the common place, can I object that legally..? How..?

Pl. check the attached jpg for clear understanding of common area occupied..

Thank you in advance..

Regards

SAthish