Validation on "Fill Job Requisition" Action

Summary:

Can we write warning/error type validation rules for "Fill Job Requisition" Action while filling a job requisition?

Content (please ensure you mask any confidential information):

We have some custom DFF fields(non-mandatory) which needs to be filled by recruiter before they go ahead and close the job requisition using "Fill Job Requisition" Action. However, recruiters usually forget to fill the relevant information in the fields under DETAILS section.

We wanted to write a validation rule such that whenever recruiters take "Fill Job Requisition" Action and if those custom DFF fields are blank then a warning/error message should pop-up on the screen preventing them to fill the job req unless user update the values for DFF fields under DETAILS section