Is it necessary for the Govt. Department to obtain registration under  GST ?

As per Section 2(73)(g) of Revised Model GST Law person” includes— any corporation established by or under any Central, State or Provincial Act or a Government company as defined in section 2(45) of the Companies Act, 2013 (18 of 2013);

Thus In case the Government organizations are required to deduct tax at source under Section 46 of Revised Model GST Law, they shall mandatorily obtain registration under the GST Act.

As per paragraph 6 in SCHEDULE V  of the Revised Model GST Law, the following categories of persons shall be required to be registered compulsorily irrespective of the threshold limit:

(vi) persons who are required to deduct tax under Section 46 whether or not separately registered under this Act;