An Employer Identification Number (EIN) is a unique identification number assigned to a business entity so that they can easily be identified by the Internal Revenue Service. Non-profits (or their fiscal sponsor) will have one, but non-federal political campaigns may not. If you don't have an EIN, it's just a matter of figuring out whatever entity identification number you use when reporting to the IRS (this may vary by jurisdiction), or if you're based in Canada, whatever number identifies the entity with your tax body.