Tds on retention amount deducted from employee salary

We are engaging technical employees and --

1) deducting some amount say 5-10% of their monthly salary  as Retention. On leaving the after 3 years we are returning to them. Whether TDS to be deducted on Gross salary to them with considering Retention amount ?

2) If employee leaves organisation before commitment period and Company forfeit his Retention amount, then what about TDS if already deducted. Employee says, I left the Company and you forfeited my Retention amount due breach of commitment period. You should not deduct TDS on that amount.

Please advice