there is a misconception that if you are hired by a Govt or semi-Govt company, you dont need an NOC from the previous sponsor.

it is partly true.

it depeneds upon the position / qualification and the urgency the new employer needs you.

for example, if you are senior consultant for instrumentation engineering / process engg, may be you can change easily without NOC

but if it is an administration, i dont think, the new employer will fight so hard for you