How to validate a cck field before printing?

Question

I have a custom content-type with a text field that has several allowed values.

There also is a printer friendly link to print.node-XXXX.tpl.php.

If one particular allowed value is selected, I do not want the user to be able to print the content without going back and editing / re-selecting a different value.

How can I set up a validation for this that will bring up an error message after the print link has been selected if that one particular allowed value is present.

Thanks