What if my W-9 has my social security but my taxes are filled out with my TIN?

[pecantree]

When filling out a W-9 for an employer, should I use my name and social security number, or should I use my business name and EIN? Even if my business is completely unrelated to the job I did for this employer?

[rjs]

You don't give a W-9 to an employer. You give a W-4 to an employer. If the person or company that you did work for wants a W-9, they are treating you as an independent contractor, not as an employee. They are your client, not your employer. Any income you receive as a contractor is business income.

If you have another business that is "completely unrelated," maybe you have two businesses, and need another EIN for the second business.

It's always best to put your EIN on a W-9, to clearly show that it is business income, and also to avoid giving out your Social Security number unnecessarily.

[Opus 17]

When an employer wants to verify your work eligibility, they give you an I-9.  Then you give them a W-4 to establish your payroll withholding.  Both of those should use your SSN even if you have an EIN for your self-employment.