When hiring vehicles to a government department, the GST payable depends on your Input Tax Credit (ITC) availability. If you claim limited ITC, you'll pay 5% GST. However, if you can claim full ITC, the applicable GST rate increases to 12%. The discussion also touches upon the Reverse Charge Mechanism (RCM) potentially applying to this scenario.
02 April 2020
From your query, it appears that you are renting/hiring vehicle to the Government department. In such case you only need to pay the GST @ 5% if you are availing limited ITC or 12% where you are availing full ITC.