Does Google withhold AdSense earnings for tax purposes?
When a website publisher enrolls with Google for an AdSense account, it is required to fill out an IRS Form W-9 and return that form to Google. There is a box on that form where the website publisher can indicate that it is not subject to backup withholding. If you do not check this box, Google will withhold 28% of your AdSense earnings and pay those withholdings directly to the IRS.