Do you know who you're doing business with? Whether you want to team up with another company, donate to a charity or switch suppliers, you should check their tax ID number beforehand. Also known as a Federal Employer Identification Number (FEIN) or an Employer Identification Number (EIN), this unique identifier can provide valuable insights into the companies you're interested in. The IRS uses it to identify legal entities for tax purposes. A quick EIN search is all it takes to find this nine-digit number so you can check an organization's identity and tax status.

What Is an EIN?

Any organization that has employees is required to apply for an Employer Identification Number (EIN). This category includes corporations, government agencies, charities, estates and other legal entities. The same goes for sole proprietorships that employ people.

This number has the role in identifying a business to the IRS, banks and private or public companies. Its similar in purpose to the SSN (Social Security Number) assigned to individuals. Without it, you cannot open a checking account, hire employees and file taxes.

As a business owner, you want to check whether or not your suppliers and partners have an EIN to make sure they comply with the law. You may also need this number for invoicing purposes.

Several websites allow users to verify the EIN of an employer or organization. All you need to do is to conduct a tax ID lookup online. The EIN or FEIN is a public record, so it shouldn't be difficult to find it.

Check With the IRS

In case you don't remember your EIN, you may call the IRS Business & Specialty Tax Line at 800-829-4933. This option is only available to authorized persons, such as the owner of a business, a trustee of a trust, individuals with power of attorney and other legal representatives. Also, if you're a partner in a partnership, you'll have access to this information.

Access the EDGAR Database

EDGAR provides data on foreign and domestic companies that are legally required to file forms with the SEC (U.S. Securities and Exchange Commission). This database includes more than 21 million filings. Users can access it for free.

For a quick EIN lookup, go to SEC.gov and click More Search Options below the search bar on top of the homepage. Enter the organization's name in the designated field under Search Company Filings. Another option is to access EDGAR search tools and search by filing date, CIK (Central Index Key), ticker symbol and other criteria.

Conduct an EIN Search Online

Real Search, FEINsearch, EIN Finder and other commercial databases allow users to check companies from all over the U.S. To verify an EIN, it's necessary to register and pay a monthly fee.

FEIN Search, for example, features three membership plans. Small business owners who sign up for the basic plan have access to 100 monthly searches. EIN Finder provides a free trial, so you can try its services at no extra charge before paying the full price.

Get Detailed Information on Nonprofits

Another helpful resource is GuideStar. The organization’s database includes information on over 1.8 million IRS-recognized, tax-exempt companies. Users can register for free to check a nonprofit's annual reports, obtain its contact information or conduct an EIN lookup. A similar resource is Melissa Data, which provides information on non-profit organizations.

There are many other ways to verify the EIN of a business. It all comes down to your particular situation. For example, if you need to check your former employer, you can find his tax ID number on one of your W-2 Tax forms or contact the accounting department. A more expensive option is to hire a private investigator.