Is it legal for a company to withhold payment for an invoice because they require an 'updated" W-9 each year even if info has not changed? They have a w-9 for the vendor. Its my understanding W-9's do not expire.
It is legal to request an updated W-9 form. The form includes a certification of accuracy (see p. 2). A payer can be liable for backup withholding, and that is a fact that can change from time to time for a payee. By requiring a fresh form every year, the payer reduces risk of liability (you have to re-swear under penalty of perjury to the same stuff). There is no direct legal obligation that a payee must inform of their change of address, name, EIN etc (they won't send you to jail if you fail to provide the relevant information). The sworn statement is how the payer knows that nothing has changed.