transportation

I dont think that there is specific section which specifically provides for a Volutarily Registered person to charge GST.

However you can look up Sec 25(3) which says "A person, though not liable to be registered under section 22 or section 24 may get himself registered voluntarily, and all provisions of this Act, as are applicable to a registered person, shall apply to such person."

Also the threshold limit of 20 Lakhs is only for registration not for levy or collection of GST

When you read Levy and Collection, Sec 9 (1) says - the tax shall be "....collected in such manner as may be prescribed and shall be paid by the taxable person."

You may further look up the definitions of taxable person as given under sec 2.

Hope this helps

Cheers!