No W-9 - reclaim withheld tax??

[phpinfo]

I received a check for stock shares in a private company. They withheld 28% because I didn't give them a W-9, but I am not subject to back withholding. How do I get that 28% back when I do my taxes at the end of this year? What for is needed etc.?

[FlyingRon]

The backup withholding will be shown on a 1099 at the end of the year.
You add this into the taxes paid and it increases the refund (or decreases the payment required).

If you don't support the W-9, they don't know you are not subject to the withholding. Withholding has nothing to do with tax liability. You get back what ever payments/withholding you have made that is in excess of your liability.