The I-864 is required even if you did not file taxes. Be sure to request IRS tax transcripts even if you did not file, to show which years you did file. It will not be fatal to your application if you did not file and did not have to but you will have to explain why you did not file taxes. Moreover, if you do not meet the requirements to sponsor your spouse under the federal poverty guidelines on your own you will be required to obtain a joint sponsor. Be advised that assets also count toward the income requirement and equity in a house or other property should be indicated on your I-864. The I-864 is a complicated little form which has a lot of hidden not-so-easy-to-understand peculiarities and issues and that is why it is a good idea to consult a competent immigration attorney especially if a joint sponsor is needed. Also for your joint sponsor and you it is very important to understand what you are agreeing to when signing the I-864. Read carefully the form, instructions and seek help.