Service tax applicability on goods transport by road service

Sir, 

I have been providing clearing & forwarding services under business support service. I want to know whether i am liable to charge service tax on freight charged by me from the Importer for Transportation of goods by road from Mumbai Port to Kanpur. I have been availing this service as input servise from GTA & paying service Tax on that & providing the same at higher freight charges to my client.

Thanks & Regards ;

Khurram