Can we add the 10% fee as stated in our Terms and Conditions to an Intent to Lien?

We have a customer who decided not to pay the final balance owed and then charged back the deposit amount. In our Terms and conditions, it states: " A late payment assessment of 10% will be added every 30 days for unpaid invoices. After 90 days an intent to lien procedure will begin." In the Intent to Lien, should we add that 10% late payment fee or should we wait until should we wait for the Mechanics Lien to add that fee?