How to prevent agent action if a linked CRM date field is in the past

How to prevent agent action if a linked CRM date field is in the past

We have support contact dates. These dates are held in CRM and are linked into Desk.

I want to prevent agents from taking action on the ticket if the support contract date is in the past.

This could be by disabling a button, showing a popup, anything really so long as it gets the agents attention.

What would be a good solution?

Cheers

Kurt