I'm a self-employed freelancer. Last year, my main client required that I get an EIN. The IRS says I don't need one and shouldn't use one. Will this complicate my taxes?

I don't think it will matter as long as you report the income. Having an EIN does give you the option of using some pension plans (KEOGH). It also lets you give out your EIN instead of you SSN to clients. Since you already have it, I would suggest just being sure to enter it on your schedule C and report the income. You should be fine.

Thank you

You do want an EIN because it saves you having to give your personal SSN to your clients (which is a security and identity theft risk).

Report all your income on one tax return.  It doesn't matter if some 1099s use your SSN and some use your EIN, the IRS knows that both numbers belong to you.  

Thank you