Look this NOC letter depend on the company owner not the qatary sponsor.
some company dont have any objection to give this letter and some yes.
if you hear this word the door ho bring air close it and have rest and that what all company doing it.
when a company start to give this letter to the labor she will have a big problem.
why? because some labor come to work here and they dont know how to work,when the company teach them and when they learn the job they will ask for leave that is the answer on your question.

Best Regard hope i respond on your question!!!