TDS on Transporters (Sub Contract)

Kindly solve my quiery:-

Normally there is no TDS on Transporters but when there is no pan number available from transporters 20% flat is to be deducted, But my Question is that this flat deduction of TDS on transporter is to availed after considering basic exemption limit (i.e. on single transaction of 30,000 or p.a. aggregate 75,000.) or without considering this limit??????