If by undocumented you mean entered without inspection even being married to a US citizen doesn't make you automatically able to file immigration documents. In fact, you might just get deported. Call an attorney to see if you're eligible to file before you do anything.
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Depends on the status of both parties and how the undocumented entered the US.
You should retain an experienced immigration lawyer to review all the facts, advise you, and handle the case. You can find one through http://www.ailalawyer.com.
J Charles Ferrari Eng & Nishimura 213.622.2255 The statement above is general in nature and does not constitute legal advice, as not all the facts are known. You should retain an attorney to review all the facts specific to your case in order to receive advise specific to your case. The statement above does not create an attorney/client relationship. Answers on Avvo can only be general ones, as specific answers would require knowledge of all the facts. As such, they may or may not apply to the question.
Depends what undocumented means for you. If it means a person who had barged into the USA through the border, it means you will need to see an immigration attorney to discuss a waiver option.
Do not do anything or submit any paperwork before consulting with an immigration attorney.
If your undocumented immigrant spouse entered the country illegally they may need to apply for a waiver. If they are approved for a waiver they still may need to leave the country for a period of time before reentering again. This process is complex and will require the assistance of an attorney.