Federal immigration law requires that employers verify that the social security numbers presented by the employee to the employer are legitimate. Employers who look the other way knowing that they have been given a bogus social security number technically face consequences for doing so.
As to telling others (like creditors) the social security numbers of your employees, you run the risk of violation of the employee's privacy rights by sharing that information with anyone other than the taxiing entities to which you are paying the employee's withholding amounts. Social security numbers are considered very private. Treat them as carefully as you should medically private information of an employee.
Good luck to you.
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