If you received a CP508C notice, the IRS has identified your tax debt as “seriously delinquent” and has provided that information to the State Department. The State Department generally will not renew your passport or issue a new passport to you after receiving this certification from the IRS, and they may remove or place limitations on your current passport.
If you received a CP2000, it means that the IRS thinks the income and/or payment information they have on file doesn’t match the information you reported on your tax return. This could affect your tax return; it may cause an increase or decrease in your tax, or may not change it at all! So what should you do if you receive a CP2000?