We recommend making copies of your EIN Confirmation Letter (CP 575) as it will be issued only once by the IRS. If you lose your EIN number, retrieving it is a tedious process which involves calling the IRS and requesting an EIN Verification Letter (147C). It will be sent to you via mail or fax which could take several days to 2 weeks. Alternatively, look through your old financing documents or tax returns that you may have recorded the EIN on.