There are over a million nonprofits in the US and many more in Canada and across the world. Your organization's Tax ID or EIN number is the unique identifier that allows donors to ensure they're selecting the right nonprofit when they request for their donation to be matched. It's the easiest way for donors to find your nonprofit when they submit their matching gift requests electronically and is sometimes required on paper matching gift forms.
Don't worry about sharing this. It's publicly accessible information available through IRS records, Guidestar, Charity Navigator, and many other sources.