There are no tax implications when dealing with a sole proprietorship or single member LLC reported on SCH C as a part of your personal 1040 tax return. In fact, I highly recommend it. I've been self-employed with my own single member LLC for 15 plus years now and there's a reason I use an EIN with my business, and not my SSN.
Occasionally I will have vendors and clients that will request a W-9 from me, which they need for their own tax reporting needs and to issue me a 1099-MISC if they are required to do so. Under no circumstances and with absolutely no exceptions will I provide them my SSN. They get the EIN only or can take their business elsewhere.
Giving my SSN to what could be someone I don't know is an open invitation for identity theft. So they only get the EIN. That way, if my EIN is used fraudulently (which while not difficult to do, is not as easy as using an SSN fraudulently) the only thing impacted is my business, and that's pretty much it. Whereas if my SSN is used unscrupulously, that can ruin my entire life.
Since EINs are issued by the IRS directly, the only ones that know what specific SSN number the EIN is tied to, is me and the IRS. That's it, because nobody else has a "need to know" that information.
