Pledging of shares in call option shorting

For Futures and Short Option position the margin requirement now increases only on expiry day, to 40% of the contract value or SPAN + Exposure margin, whichever is higher. You can check out this post for more information: Relaxation in Physical Delivery Policy - Margins collected

If you want to give delivery of shares, it is best to unpledge them before expiry day so avoid risks of short delivery.